CHAPTER IX. 183

PARASITES THAT UNDERGO TRANSMIGRATIONS AND METAMORPHOSES.

A certain number of parasites establish themselves at first in an

animal which serves as a _crèche_, then in a second which serves

as a lying-in hospital. This passage from one animal to another is

described under the name of transmigration. In general, the entire

_crèche_ with its nurslings passes into the lying-in asylum. The

_crèche_ is always represented by an animal which feeds on vegetable

diet, which is destined for one which is carnivorous: the lying-in

asylum is represented by the latter. The mouse is the _crèche_ which

will pass with all its clients into the cat which eats it.

If we were treating of plants, we should say that in the first host

they are developed, and in the second they blossom. The plant, like

the animal, is agamous as long as the flower and the sexual organs

have not made their appearance.

The animal which migrates usually undergoes a complete change in

passing from one abode to another; it is agamous in the first

instance, that is to say, without sex, swathed and covered with a

padded cap like a nursling; in its last stage it is, on the contrary,

endued with all its sexual attributes.

In the _crèche_ the parasite is on its passage from one station to 184

another, and that which arrives at the lying-in asylum has reached the

end of its journey and is at home. We have proposed to give it the

name of _Nostosite_, as distinguished from that which only inhabits

its host for a time. We may also remark that the same animal may give

lodging to these two kinds of parasites. It is thus that the rabbit

harbours in its peritoneum passengers which are only at home in the

dog; and, independently of these passengers (these strangers may we

say?), it lodges in its intestines a sexual tænoid worm. The first is

a _Xenosite_, the second a _Nostosite_. The mouse, in the same manner,

gives lodging to passengers under the name of _Cysticerci_, which are

destined to the cat in order to become _Tæniæ_.

We might call the rabbit or the mouse which harbours worms _in

transitu_, the stage coach; more especially as from time to time there

are some which miss it, and are consequently lost in their

peregrinations.

This stage-coach is the intermediate host, the _Zwischenwirth_ of

German helminthologists, which is always an animal with a vegetable

diet; the final host is generally a carnivore: it is by means of the

vegetable feeder, the grazing or herbivorous animal, that the stranger

parasite introduces itself.

The result of this is, that the carnivore receives into its house,

every time that it devours its prey, all the parasitical inmates of

the latter, and the walls of its digestive canal form the soil in

which are implanted all the worms which can take root there. The

tissues of the prey are triturated and digested, but the worms which

it encloses escape the action of the gastric juice, and are set at 185

liberty in the stomach. The stomach of the carnivorous animal is a

sieve through which thousands of parasites are often introduced at

each repast, and fishes lodge many which often pass from one stomach

to another. Their whole life is spent in these migrations; they are

travellers who have their abode in railway carriages, and never take

their departure at the stations.

Each stomach is, in fact, a station, very frequently quite filled with

merchandise, which disappears with the station itself by the next

train. Happy are those who find themselves in a carriage safely on the

rails towards its destination. Many are called but few chosen. How

many journeys some of these travellers have to take before they find

their host!

It is often very interesting to open a fish which has made a good

meal; its stomach and intestines contain, first of all, the usual

worms; the half-digested prey, in its turn, encloses some; and it is

not rare to find besides them the parasites of those which were

swallowed together with their host.

The animal is usually attacked in its youth by the parasites which it

harbours all its life. In order to know the inhabitants of some

fishes, we must examine them shortly after they are hatched.

In the _crèche_ the parasite occupies an organ which is closed, and

without communication with the outer world; it inhabits the garret of

its first host; in its last host, which represents the maternity

asylum, it dwells, on the contrary, in the largest apartments, and

never ceases to be in direct communication with the exterior. Thus, in

the first animal, it is often completely immovable and under a form

which we have named _scolex_; in the latter it moves freely, and has, 186

in addition to sexual organs, those which are proper to this condition

which we have called _Proglottis_. Thus these parasites undergo

metamorphoses.

For a long time, metamorphoses seemed to be the attributes of frogs

and insects exclusively. In the class of worms, in which they are

complicated with the change of hosts, they much surpass in reality the

most brilliant and extravagant fictions of the poets. The phenomena of

these transmigrations were completely unknown before our researches

were made. If some naturalists, like Abildgaard or Pallas, suspected

their existence, it was rather by accident, and the experiments to

which they devoted themselves were all unfavourable to their

suppositions.

The knowledge of these transmigrations has at the same time dispersed

the latest illusions of the partisans of spontaneous generation; it

was the more difficult to explain the presence of worms in enclosed

organs, since these worms were always without sex. By the same means,

we have ascertained the true prophylactic treatment, and thus

discountenanced the numerous anthelminthic remedies which had often

caused more serious accidents than the parasites themselves.

When it was considered that parasites were the result of an especial

degeneration of some of the intestinal papillæ, the physician would at

once consider that there was some morbid condition, and we can

understand that all his efforts would be employed against the enemy

which had arisen. Now it is known that every healthy animal living in

freedom contains parasites almost as invariably as the organs which

support its life; and it is not a matter of doubt to us that 187

parasites often play their allotted part in the economy; their absence

as well as their presence may be the cause of inconvenience. We should

not even be astonished if the administration of certain worms

internally should be prescribed as a remedy. Have we not known the

time when all maladies were supposed to yield to the action of

leeches, and do we not see the good effects of their application?

There are many kinds of parasites, and their therapeutic effect may,

perhaps, in future, form an interesting subject of study.

To speak at the present time of a verminous temperament would be

scientific heresy, an anachronism; this shows the progress that we

have made of late years. Valenciennes was permitted to employ this

language at the Academy of Sciences in Paris not twenty years ago, and

Lamarck wrote thus in his standard work on invertebrate animals, in

the beginning of this century: "It is very certain that there exist in

a great many animals, and even in man, intestinal worms; some of which

are formed there, others are born and all live there, multiplying more

or less, without any of these worms showing themselves externally, or

being able to live elsewhere.

"During so many centuries that observations have been made,

well-ascertained species of intestinal worms have been found nowhere

else than in the bodies of animals. We are now authorized to believe

that there are _innate_ worms, or such as are produced by spontaneous

generation, and that these are modified from time to time; this is at

present the opinion of the most enlightened observers."

Thus it was considered by Lamarck that parasitical worms are only 188

found in the bodies of animals, and are actually produced there.

Can it be believed that such ideas were put forward by zoologists of

the highest merit? and ought we to feel surprised that the theory of

spontaneous generation was so long taught in the physiological

schools?

A book published in 1859 was entitled, "Heterogenesis, or a Treatise

on Spontaneous Generation." The author gives the clue to the origin of

his errors in the second line of his preface, in which he says: "When,

_by meditation_, it was evident to me that spontaneous generation

was one of the means employed by matter for the reproduction of living

beings."... According to this philosopher, science is, therefore, not

the generalization of facts, but these facts must serve to prop up the

theories or hypotheses invented in the silence of the study. This

passage of his work shows us that he was no more able to yield to the

evidence of experiments made on worms, than to those of Pasteur on the

infusoria.

It may be related to the honour of the illustrious Baer, that, from

the year 1817, during his stay at Königsberg, he took up arms against

this hypothesis, and never ceased to combat it, till evidence

succeeded in opening the eyes of the most obstinate.

The worms which present the most remarkable phenomena of transformations,

accompanied by metamorphoses, are the Distomians and Cestodes, flat

worms, which we will consider in the first place.

Trematode worms include a certain number of large and beautiful

parasites which scarcely undergo any change, and are found only on the

skin and the gills of certain fishes; these are the monogenetic 189

trematodes, comprising the _Tristomidæ_ and all the worms of that

group, which also stand higher in their organization: we shall speak

of them hereafter. The other trematodes, which are called digenetic,

live on the most dissimilar animals, under the most varied forms, and,

like the greater part of the cestodes, introduce themselves into the

individual who is to give them shelter, only by the assistance of a

host, acting as a stage-coach which serves them as a vehicle.

The principal family is that of the Distomidæ, a family _par

excellence_ cosmopolitan; as inconstant in their progress as

capricious in the choice of their companions. Each distome resembles a

small leech which has a sucker in the centre of the belly, and as this

sucker was once considered to be perforated, the name of Distoma was

given to them.

These parasites are the more interesting to us, from the fact that,

though we are not the final resting-place of certain species, we

nevertheless find them pass through us on their way. There are two

species which occasionally lodge in the liver of man without being

peculiar to him, for they properly belong to the sheep. Two other

distomes have lately been described by Dr. Bilharz, which are

fortunately only known at present in Cairo, and which are interesting,

both with respect to their organization and to their manner of life.

The genealogy of the distomidæ is now generally well known; that which

remains to be discovered is the itinerary of each particular species;

and in several zoological laboratories experiments are daily made with

certain species and the hosts which they are supposed to seek. These 190

These investigations have already yielded the best results in the

laboratories of Giessen and of Leipzic, under the direction of

Leuckart.

The genealogy of the distomidæ is as follows: the young distome, when

it leaves the egg, is wrapped in a ciliated tunic, and, under the

guise of a microscopic infusorial, it abandons itself to all the

vagaries of a free and vagabond life; this is the bright period of its

life. "It is a youth starting, with all the steam up, without help and

without guidance, in the midst of the ocean; if it meets an island on

its passage, that is to say, the body of an aquatic larva or a

mollusc, it disembarks, brings forth its young, and disappears; its

purpose is fulfilled. If it find no island or continent it sinks and

perishes, for it carries no provisions with it; it has no organ which

permits it to take nourishment on its passage." If life is short, even

in the case of a young distome, it is passed in the midst of the

water: if fortune is favourable to it, it will at last meet with a

living abode, where it will find all that is necessary to the comfort

of a parasite.

Abundance always reigns in these living oases; and as these new

colonists are really exiles, who will never again see their native

country, ciliary oars are useless to them, and their descendants

differ entirely from their common mother.

Under the ciliated tunic of the mother appears a daughter under the

form of a bag, who is born almost at the same time as herself, and

concerning whom we may quote here the words of Réaumur: "Singular and

mysterious duality in unity; two beings, living one within the other,

which are still only a single individual. Has nature accustomed us to

such profusion? Do we ever see her retrograde thus from a more 191

complicated organization to one more simple?" That which this great

observer did not dare to believe has yet been realized, and in many

cases development is clearly recurrent.

Led by a marvellous instinct, and obeying an irrevocable mission, the

distomidæ, as well as the monostomidæ, and others besides them, when

they claim an asylum from molluscs, introduce into the living body of

their new host, not an isolated embryo, but a young animal already

impregnated with a rich posterity; if she remain mistress of the

situation, this posterity will forcibly invade the various organs,

without any consideration whether their host may not give way under

the weight of this sudden invasion.

[Illustration: Fig. 41.--Monostomum verrucosum, Sporocyst with

Cercariæ. In front is the mouth, in the middle the digestive canal,

and around the digestive canal are young ones, under the form of

Cercariæ in process of development.]

Fig. 41 represents one of these worms which proceeds from a ciliated

embryo, and encloses by the side of its digestive tube cercariæ in

different degrees of development. In front, we see one provided with

eyes and a tail; behind, we see others which are younger; among these

ciliated embryos, wandering without guidance and without a compass in

the midst of their ocean, but few will reach the land, or, in other

words, will find the port where their progeny may prosper. This 192

first embryonic state is that in which there are the greatest perils.

When stripped of their swimming tunic, these young distomes have the

form of a bag, which for a long time was called a _sporocyst_. From

these sporocysts we see hundreds and thousands of young ones proceed,

resembling in no respect the mother which has brought them into the

world. These, in their turn, will resume a free and independent life.

They are colonists whom the distome has left on a foreign land. This

simple multiplication is often not sufficient for the preservation of

the species; the first sporocyst produces other similar sporocysts,

and these bring into the world a rich progeny of tadpoles, which after

a certain metamorphosis will become sexual distomes. These tadpoles

are often well armed, and devour occasionally even the last scrap of

flesh belonging to their host. They have long been known under the

name of Cercariæ, which was given to them at a time when their

genealogy was unknown. They are not very unlike the tadpoles of the

frog (Fig. 45). The mother was only a bag with ciliæ, and sometimes

with eyes. The tadpole has a distinct body, with a movable deciduous

tail; and after this falls off they have sexual organs.

The cercariæ often abandon their first host in which they have been

developed, and live at liberty in the water while waiting for their

final host. They are taken sometimes in the open sea. In 1849, J.

Müller wrote to me from Marseilles that he had just discovered

cercariæ and distomes living at liberty in the Mediterranean. Since

then this illustrious naturalist has observed them again at Trieste,

while pursuing his studies on the Echinodermata, and has had the 193

kindness to send me his original drawings of these singular parasites.

We have found both at Marseilles and at Trieste, says J. Müller, a new

cercaria with a pinnate tail, and two black ocular points; its body is

from one-tenth to one-sixth of a line in length, not including the

tail, which is twice or two-and-a-half times as long. There is a

protuberance just in front of the middle of the body. At each side of

the tail there are from twelve to twenty pencils of soft bristles

placed on little prominences in a transverse series of six tufts, not

regularly opposed to each other. In one specimen, the tail, from its

point of insertion to the posterior quarter, is provided with these

bundles of bristles; and in another they are wanting entirely in the

anterior half, but exist, on the contrary, on the hinder half. In a

third, the bristles have partially disappeared, and are reduced to six

bundles at the extremity of the tail. This tail presents traces, more

or less distinct, of transverse rings. J. Müller has often seen that

the distome, which proceeds from this cercaria, swims freely in the

sea, and after having got rid of its tail, could be easily recognized

by the two black marks which were then more diffused.

This cercaria described by J. Müller recalls to us that which was

noticed by Nitzsch on fresh-water shells (_Cercaria major_) with an

annulate and pinnated tail.

Claparède also took at Saint-Vaast, cercariæ the host of which he did

not know. This naturalist supposed that this worm could migrate at

will. He found there the same cercaria (_C. Haimeana_) on Sarsiæ and

Oceaniæ, but always sexless.

The _Cercaria setifera_ of J. Müller has been found free and attached 194

to the lower surface of some medusæ. It exists occasionally in

considerable numbers on the internal surface of some Acalephæ of the

ocean and of the Mediterranean. Claparède has also observed another

free cercaria which bears the name of _Pachycerca_.

Some of the cercariæ are very tenacious of life; we have kept some

alive in fresh water during a whole week in the month of November, and

on the last day they were still active (_Cercaria armata_). We

sometimes find the cercarian age passed over, and the young distomes

appear abundantly without tails in the sporocyst. We have seen an

example of this in the _Buccinum undatum_ of our coasts. This latter

generation assumes in every case a very different form from that which

preceded it.

Lodged and nourished without expense in the succulent parenchyma of

their victim, the cercariæ grow rapidly, and as soon as their caudal

oar is developed, they tear asunder the membrane which encloses them,

and abandon their host in order to live freely as tadpoles. Some fine

day, tired of their nomadic life, they choose another host, get rid of

their tail, fold themselves up in a winding-sheet, like a chrysalis

about to become a butterfly, and concealed in a sac, which is

designated by the name of cyst, they wait patiently for days, weeks,

or years till their host is swallowed by the creature intended to

lodge them. The cyst is set free in the stomach of the latter host,

its envelopes are dissolved in the juice secreted by its enclosing

membrane, and with its whole establishment the worm recovers its

liberty in this new abode.

The encysted cercariæ pass thus with arms and baggage into the stomach

of a new host. Their envelopes, not to say their swaddling-clothes, 195

are torn to pieces by the gastric juice, and at the end of their stage

they go and lodge in larger apartments, more appropriate to their new

wants. The time of their celibacy is passed, and a numerous progeny,

under the form of eggs, is prepared. In this condition they fulfil

their last mission; and if their mother, the sporocyst, knew only the

joys of agamous maternity, the cercaria which has just become a

distome appreciates all the sweetness of sexual maternity.

The distome thus reaches the termination of its voyage and of its

evolutions; it lays its eggs in the midst of the feces of its host,

and millions of animalculæ watch for the new brood, while others wait

for the visit of the ciliated generations. The daughter distome thus

differs completely from her mother sporocyst, but she resembles her

grandmother who has lived in the same manner as herself. Thus we have

animals free and vagabond when they leave the egg, and which swim

vigorously like infusoria without depending on others. But the end of

their life approaches, they strip themselves of their ciliated mantle,

and being again closely swathed up before they die, they seek the

hospitality of a mollusc and give birth to their numerous progeny.

We have therefore animals whose little ones in swaddling clothes live

at first at liberty, and seek for assistance when the moment for

thinking of a family approaches. The descendants lead, like their

parents, a wandering life; and as their mother threw off her ciliated

cloak, so they abandon their oar-like tail, to think in their turn of

family cares.

To sum up all, there are in the life circle of a distomian two 196

distinct forms, which begin and end in the same manner, the first

putting forth a progeny by means of buds, the second by eggs. There is

alternation of form, on account of the double multiplication

(digenesis) and migration through several individuals. In other words,

the young distome, before it reaches its destination, must change its

train many times, and it wears in each carriage a different costume.

We can easily understand how difficult it is to recognize this

travelling distomian, as it changes continually its railway-train and

its dress, and what sagacity must have been employed by naturalists in

order not to lose its track.

We may give more than one description of the distomian embryo as it

leaves its sporocyst. Is it a mother and an enclosed daughter, as is

the case with aphides, or is the ciliated envelope merely a cloak? We

think that the latter is the true interpretation. The ciliated mantle

which the embryo loses, is a skin which has been thrown off in

moulting, a simple effect of age.

Thus we find in the complete evolution of a distome an organic and a

sexual age, a true alternation; the agamous age undergoes a true

moulting, the sexual age a metamorphosis.

We have before considered the embryo as mother and daughter coming

into the world together, as we see among the aphides; or the mother,

daughter, and granddaughter are born together like twins; so that if

the mother or the daughter meet with an accident during parturition,

the granddaughter may be born before her mother, and even before her

grandmother.

We are now about to study some of these mysterious travellers which

have given so much trouble to naturalists to discover their abode 197

and determine their identity. Considering the number of observers who

have mentioned these distomes, it is evident that these parasites must

be very common. We find the names of Ruysch, Leeuwenhoek, Swammerdam,

Camper, Houttuyn, Mulder, Heide, Biddloo, Snellen, etc., among the

naturalists who have made them a subject of study. In our own day, the

writers who have explored this territory are so numerous that we

should require more than a page simply to give their names.

Distomes frequent, with few exceptions, all the classes of the animal

kingdom, and if their number is great among fishes, they are not less

numerous in mammals and birds. The higher classes of animals usually

inoculate themselves through the intermediation of molluscs, worms,

and crustaceans, and it is therefore in the ranks of these that we

must seek for their first abode. Without admitting that their size

bears some proportion to the host which gives them shelter, still, the

largest species, the _Distomum Goliath_, is found in the liver of one

of the balænoptera. This distome is of the size of a large leech, and

its host does not measure less than twenty metres.

Mons. Willemoes-Suhm mentions a distome which at the time of its

cercarian evolution lives freely in the water, and attaches itself by

its sucker to the larvæ of worms or copepod crustaceans, and then

lodges in their dejecta without encysting itself. This is the

_Distomum ocreatum_ of the herring, according to Professor Moebius.

Mons. Ulialnin found in the bay of Naples another free distome, which

is also attached by its ventral sucker to certain copepods, and which

becomes the _Distomum ventricosum_ inhabiting many kinds of fish.

Any one who wishes to make observations on distomes in the state of 198

cercariæ has only to examine some fresh-water molluscs, either the

Limneæ or Planorbes found in ponds; as he tears the animal to pieces

on the stage of a simple microscope, he will not fail to perceive a

multitude of struggling and wriggling tadpoles. Their tails twist with

each other, furl up, extend, and describe arcs of circles, as if we

had a nest of serpents under our eyes.

Each species of distome has it own cercariæ, which are scattered among

as many different inferior animals. Birds and fishes become infested

by them in consequence of eating these animals.

[Illustration: Fig. 42.--Liver fluke of twice the natural size; _a_,

mouth; _b_, penis; _c_, digestive tube; _d_, abdominal sucker.]

We may here cite as an example of this class of parasites the

_Distomum hepaticum_, or liver fluke; this species is the most

interesting to us of all the genus; it attains the size of a moderate

leech, and habitually resides in the liver of the sheep. In order to

discover it, we have only to examine a fresh liver. They are usually

found in the biliary canals, where they move about like planariæ. It

is always of a deep colour, and is doubtless introduced in the state

of cercaria, when the animal is drinking. M. Willemoes-Suhm supposes

that the _Distomum hepaticum_ has for a vehicle a small snail, the

_Limax agrestis_, which the sheep swallows with the grass on which it

feeds. Its principal abode is in the ruminants and only casually in 199

man. It is said to be unknown in Iceland. The _Distomum lanceolatum_

has also been found in man.

Dr. Bilharz, the pupil of Siebold, discovered in the year 1851, on

man, a parasite in every respect remarkable. It belongs to the family

of the Distomidæ, and on account of its peculiarities, it has been

made into a genus under the name of _Bilharzia_. It is found in Egypt,

and lives in the vena portæ and in all its ramifications in man.

According to Bilharz, this distomian is dioecious, the male being of

considerable size, the female slender and delicate, which fact does

not agree with the usual characteristics of dioecious animals. At

least half of the Fellahs and Copts suffer from these parasites; these

worms, at the period when they lay their eggs, proceed from the vena

cava to the veins of the pelvis, and after having produced very grave

consequences, they are at last evacuated with the urine.

Another distome was also found by Bilharz in the intestines of a young

Egyptian boy.

The largest known distome inhabits the liver of the _Balenoptera

rostrata_, the little whale of thirty feet in length, which is

regularly met with on the coast of Norway. The intestines of the

ordinary seal often contain a very curious distome, which was first

observed by Rudolphie, the _D. acanthoides_. The seal is also infested

by the _Distomum cornus_, which some have incorrectly preferred to

place in the genus Amphistoma.

Besides the distomes which inhabit the liver, there are found but few

in the mammalia, except in the Cheiroptera: these insectivorous

animals have their intestines literally full of these parasites. We 200

have noticed the species which regularly frequent our bats, and it

only remains to discover the insects by means of which they are

introduced; for it is probable that these insects are infested by

cercariæ during the time that they inhabit the water. Larvæ and their

parasites ought to be carefully studied in the localities where bats

abound.

There are few birds, especially among the grallæ and the palmipedes,

which do not enclose in their intestines a certain number of distomes.

The same may almost be said of reptiles and batrachians, but it is

especially in fishes that their number is greatly increased. We may

say that there is no fish which does not nourish some of these

trematodes. Among a portion of these, the cycle of evolution and

transmigration is perfectly known; we may instance the _Distomum

nodulosum_. This worm inhabits the intestines of the perch.

The scolex, as well as the cercaria, has its particular characters,

and we have long since found the latter in a fresh-water mollusc, the

_Paludina impura_. The cercaria is easily recognized by the presence

of two particular folds at the base of the buccal bulb, and by the

transparency and the form of the extremity of the urinary apparatus.

In the adult distome, this same part of the urinary apparatus encloses

large vesicles with very distinct partitions.

We may also mention among the distomes a species from fish, which has

a great affinity with the singular distome observed by Bilharz, of

which we have spoken above. This distome inhabits the "castagnole," or

_Brama raii_. Under the opercula of this fish, the skin is folded, and

forms one or more pouches, in each of which lives a coupled distome, 201

that is to say, by the side of each large and fat individual, full of

eggs, there is one which is slender. It is the _Distomum filicolle_,

to which the name of _Monostomum_ was at first given. We should be

correct in supposing that of these two hermaphrodite worms one acts

rather as a female, the other as a male. It is doubtless in this sense

that Steenstrup maintained his assertion, that there are in nature no

hermaphrodites.

Thus there are two kinds of distomes: the first live in couples in a

cyst, the second in couples joined together, but at liberty; and in

each case only one individual produces eggs. These are distomes which

act really like dioecious worms. We find, however, a more remarkable

instance in the _Monostomum bijugum_ of Miescher. In the tumours which

are formed in the beak of the grosbeak (_Fringilla_), he has

constantly found two individuals; and in many cases he has surprised

them with the penis of one engaged in the sexual organ of its

companion. These worms, while they live in couples, resemble each

other like snails and leeches; they are mutually fecundated, and both

lay eggs.

Leuckart recognized these sexual distomes in their cyst, in the larvæ

of ephemerides; and Linstow noticed a distome thus sexual and encysted

in the _Gammarus pulex_.

The name of Monostoma has been given to some of these trematodes which

have no abdominal sucker.

One of the most curious worms of this group is the _Monostomum

mutabile_. It lives in the sub-orbitary sinus of several aquatic

birds; that is to say, in the nasal fossæ, especially of water-rails

and moorhens. We give a slightly magnified representation of them. It

is a worm resembling an elongated leaf. By compressing it slightly 202

on the stage of the microscope, we easily discover the ovary, the

matrix, and oviduct full of eggs. By isolating some of the eggs, and

crushing them gently to break the shell, we set free the worm (Fig.

44), quite different from the mother (Fig. 43). The former has two

eyes surrounded by a ciliated mantle, and by means of this ciliated

envelope, the monostome swims freely in the water. If we compress it

slightly, we see that in the interior of the ciliated covering, there

is still another animal, without eyes, without ciliæ, and of an

entirely different form, which in its turn encloses a whole progeny.

[Illustration: Fig. 43.--Monostomum mutabile (adult).]

[Illustration: Fig. 44.--Monostomum mutabile. Ciliated embryo with

sporocyst and young cercariæ, greatly magnified.]

The embryo, having long ciliæ in front, and in the interior a

sporocyst already full of young cercariæ, is shown in Fig. 44. It is

this latter creature which the ciliated embryo must confide to the

care of others; this she puts out to nurse with some mollusc or other,

until it is fit to provide for itself in its turn. We have still to

discover the train by which the parasite must travel, in order to 203

arrive again at the nasal fossæ which are the first cradle of the

family.

We find occasionally between the feathers of some birds tubercles of

the size of a pea, and when we open them we see in each two similar

worms, placed so that the stomach of one is applied to that of the

other; this is the monostome of which we have spoken above. These

worms are from three to four millimètres in length (about ·13 in.),

and are found in the titmouse, the siskin, the sparrow, the canary,

and some other birds.

[Illustration: Fig. 45.--Cercaria of _Amphistomum sub-clavatum_.]

[Illustration: Fig. 46.--Sporocyst of _Amphistomum sub-clavatum_ from

the _Cyclas cornea_.]

A worm very common in the intestines of the green frog is known by the

name of _Amphistomum sub-clavatum_. Its cercariæ are usually found in

an acephalous mollusc, known by the name of _Cyclas cornea_. That

which distinguishes the scolices of this species is the great

contractibility of the external membranes of the young individuals;

they lengthen, they shorten, they swing to the right and the left,

describing a semicircle on the anterior half of the body (Fig. 46). We

represent side by side the cercaria of this amphistome, and the adult 204

and sexual amphistome, as it is found in the intestines of the frog.

Constantine Blumberg has recently published an interesting memoir on

the structure of the _Amphistomum conicum_.

A beautiful trematode worm, known by the name of _Hemistomum alatum_,

whose antecedents have not been ascertained, lives usually in the

intestines of the fox. It is about four or five millimètres in length

(about ·17 in.). Many birds harbour Holostomes which belong to the

same group, the first state of which is not yet known. The _Holostomum

macrocephalum_ is common in the intestines of rapacious birds; it is

from five to seven millimètres in length (about ·23 of an inch).

We close the history of trematode worms by giving the figure of a

beautiful one known under the name of _Polystomum_, which lives

in its adult state in the bladders of frogs (Fig. 48). Interesting

observations have recently been made on the manner in which they are

introduced into the bladder.

The worms which naturalists call Cestoïds, or Cestodes (which means,

like ribbon or tape), have for their type the tape-worm known by every

one. They are very abundant in many animals, are found in almost every

class of the animal kingdom, and are almost as common as the

distomians, of which we have just spoken. They are introduced into

animals which are vegetable-feeders, by means of water and plants, and

into carnivorous animals by their prey. The tape-worms of the

herbivora lay eggs like the others, but their embryos have, as soon as

they are hatched, a ciliary covering which allows them to live and 205

move about in the water. Those of beasts of prey are entirely

different; it is by means of the prey that they enter their hosts.

Each carnivore has its own worms, as it has its own prey which

introduces them.

[Illustration: Fig. 47.--_Amphistomum subclavatum_ of the frog.]

[Illustration: Fig. 48.--_Polystomum integerrimum._]

Independently of these worms, the vegetable-feeders afford lodging to

some which are not their own.

We have found in bats two tæniæ, both incompletely developed, and 206

occupying the digestive tube. One has a rostellum without hooks, like

the tæniæ of the vegetable-feeders, the other has hooks like those of

the carnivora. These cestode parasites are observed to be of two

principal forms; the first vesicular, like the finger of a glove

partly drawn inwards. They are always lodged in the midst of the

flesh, or in a closed organ in the middle of a cyst; under this form

the cestode worm is harboured by a host which is to serve as a vehicle

to introduce him into his final host. He is a parasite on a journey;

he is always agamous, and usually bears the name of cysticercus (Fig.

49). As to the second form, it is like a ribbon; it attains a great

length, always occupies the intestine, attains its complete and sexual

development, and lays an innumerable quantity of eggs which are

disseminated with the evacuations.

[Illustration: Fig. 49.--Cysticercus; _a_, upper part of the vesicle;

_b_, place where the vesicle is about to separate; _c_, neck of the

worm; _d_, the head, showing the suckers and the crown of hooks.]

The rabbit harbours a cysticercus which has its final destination in

the dog (a xenosite); but independently of this stranger, it gives

hospitality to a special tænia in its intestines. This is its own

worm, the _Tænia pectinata_, which is a nostosite. All the herbivora

are in a similar case; the ox and the sheep possess a peculiar tænia

of their own, besides those which they lodge for the sake of the 207

carnivora. The worms of the herbivora have particular characters by

which they are easily known; they have no crown of hooks.

The tænia of the wolf, which has often been confounded with the _Tænia

serrata_, lives in the brain of the sheep, and produces a disease

known as the "gid." It was formerly said that every animal has its

enemy. We should rather say that each species has its parasites, and

each parasite has its vehicle by which it is introduced.

These tape-worms are found in all the vertebrate classes. An

herbivorous animal usually serves as a vehicle, but it more frequently

carries, besides its passengers, species which are peculiar to itself.

As the carnivorous animal is not intended to be eaten like the

herbivora, it cannot serve as a vehicle, and if by chance its muscles

enclose some passenger, he has lost his way and that for ever.

Do the cetacea generally live on fish, and do they become the prey of

some aquatic carnivora? We have reason to think so, from the presence

of certain agamous cestodes, which have been frequently found in too

great number to allow us to suppose that they have lost their way in

these aquatic mammals. There have been seen in the substance of the

muscles of many species, or rather in the layer of blubber which

covers the skin, agamous cestode worms of the genus _Phyllobothrium_,

which can only accomplish their evolution in some large _squalus_.

There must then be contests between dolphins and sharks, contests in

which the dolphins are worsted, in spite of their superiority. These

Phyllobothria have been found in the _Delphinus delphis_, the 208

_Tursio_, and the _Ziphius_. As the _Orca_ attacks the whale, and

feeds upon its flesh, there would be nothing surprising in our finding

in these large cetacea, some agamous cestode destined to pass through

the last phase of its evolution in this terrible carnivorous animal.

The cestode can scarcely be called a parasite under the first

vesicular form. It is sufficient for it to pass through its first

transformation in the midst of the tissues, and it will remain weeks,

months, even years, without undergoing any change; it asks for nothing

but an hospitable roof; and this mysterious being, that had often come

they knew not whence, encamping rather than lodging, always without

progeny, was long since cited by the naturalists of a former age in

favour of the old hypothesis of spontaneous generation.

It is not the same with the second form. Here the worm, always lodged

in the intestines, grows with extraordinary rapidity, and fulfils all

the conditions of a true parasite. In a fertile soil it extends itself

and produces young as long as it has any life, and in no group of the

animal kingdom do we find any fecundity to be compared to that of this

worm. Boerhaave described a broad tape-worm, three hundred ells in

length. Eschricht estimates the number of the segments of this worm as

ten thousand; and if we consider that each segment, or, we should

rather say, each complete worm, may perhaps enclose thousands of eggs,

we may form some idea of the profusion of germs which can be scattered

by each individual.

To thoroughly know an animal we must have made observations on it

during all the phases of its evolution. Let us sketch these phases. 209

All the cestodes have eggs, usually in great number, very well

protected against external agents. They endure heat and cold, drought

as well as humidity, resist by means of their envelopes the most

violent chemical agents, preserve the faculty of germinating, we will

not say for weeks, months, and years, but for centuries. When they

first leave the egg, we see an embryo of an oval form, transparent,

composed apparently of sarcode, contractile throughout all its extent,

and in the middle of which we perceive six stylets arranged in pairs,

and which at last move with great rapidity.

The following is the manner in which, some years since, we described

these six hooked embryos produced by a tænia of the frog, which were

struggling by the side of each other on the slide of a microscope.

"The six hooks are arranged regularly in each individual, and move

exactly in the same manner. They are very slight, and of nearly half

the diameter of the embryo. Two occupy the median line, and unite like

a single stylet; these are nearly straight, and a little longer than

the others. They only move backwards and forwards. Their action is

like that of the parts of the mouth in certain parasitical

crustaceans, the Arguli, when they endeavour to pierce through the

tissues. They are in continual motion to and fro. The other four hooks

are similar to each other, and differ from the first in the point,

which is curved into real hooks. They are arranged two and two, to the

right and left of the first, so that they all meet at the base. Their

movements are not the same as those of the two first; they remain

almost fixed at the base, while they describe a quarter of a circle at

the extremity. Let us imagine the six hooks, placed in front in the 210

same direction. The two in the centre advance, and the two pairs

placed symmetrically by the side of them, are lowered and drawn

backwards, and thus push the body forwards.

"It is like the dial-plate of a clock, with three hands placed by the

side of each other; that in the middle would advance directly forward,

while the two others would be lowered until they formed a right angle

with the first. This is the movement which we observe in all the

stylets. The result of this is that we distinctly see the embryo

penetrate between the _débris_, or into the crushed tissues which

surround it. These embryos imitate the movements of a man who wishes

to get through a window a little above him, and who, having succeeded

in passing his elbows through, pushes his body forward by leaning them

on the frame.

"We see the same efforts continue for hours; and we can easily

understand that there is no living tissue, however dense it might be,

except the bones, which could not be easily penetrated by these

microscopic embryos. This explains why we so commonly find cysticerci

scattered in cysts along the intestines and between the membranes of

the mesentery, and how they can, by piercing the walls of the vessels,

spread themselves into the most distant organs, by means of the blood

which conveys them. When the embryos have once pierced these walls,

they hollow out the tissues in all directions, until they find

themselves in the muscles, or in the organ which is indicated in their

itinerary. When they have arrived at their destination, they stop and

surround themselves with a sheath; their stylets, which are no 211

longer of use to them, decay; and at one of the extremities appears a

crown of new hooks quite different from the former ones, which will

serve to anchor their progeny in the new host into which they may be

introduced."

[Illustration: Fig. 50.--Vesicular worm.]

Thus the vesicular worm (Fig. 50), fully formed, and without undergoing

any change, waits till its host, or the organ which shelters it, is

eaten, and then wakes up in the stomach. Every living cysticercus

which penetrates into the stomach, instantly quits its torpid state:

it gets rid of its useless parts, abandons its former cavity,

penetrates into the intestine, attaches itself by its new hooks and

its suckers to the enclosing membranes, and grows with such rapidity,

that in less than six weeks, we often find a tape-worm many metres in

length. The vesicle which had hitherto protected it, is abandoned, and

the part which remains with hooks and sucker is the mother which has

produced in this agamous manner the whole colony. This mother is

usually called the head of the tænia, or more properly the scolex. As

long as the mother is there, she engenders and produces cucumerinæ,

that is to say, proglottides, which are the perfect and sexual state

of the cestode.

We have seen among the trematodes a worm of a particular form leave

the egg, and immediately produce a swarm of young ones, which go and

live separately. In the cestodes all these individuals are united 212

in a kind of band, and are besides this joined to the mother, which

becomes the root of the family. This root, planted in the walls of the

intestine, is the head. Thus each segment of the tænia is an

individual, and at the period of sexual maturity, this individual is

detached, goes away with the feces, spreads over the grass or

elsewhere, and thus sows far and wide the eggs which it contains.

The tænia, as well as the other tape-worms, is generally looked upon

as an imprisoned parasite during the whole of its existence. This is a

mistake; the last stage of the life of cestodes is a phase of liberty.

The cucumerina, or, as we have proposed to call it, the proglottis,

that is to say, the complete and sexual animal, is evacuated with the

feces; and when we notice a dog leaving his dung upon the grass, it is

not uncommon to see there worms which move like leeches, and whose

white colour is in strong contrast with the mass which contains them.

The duration of this last stage is very short, it is true; but it is,

nevertheless, during this period of her life that the mother scatters

the eggs which are to disseminate the species.

We repeat that each animal has its parasites, and these in their turn

are not always exempt from them. We have already cited some examples

of this.

Man has the dental system of a vegetable feeder; but, thanks to fire,

which he alone knows how to produce and maintain, he eats flesh. It is

by these means that he nourishes the solitary worm, which, by its

crown of hooks, is a cestode belonging to the carnivora, and the

_Tænia mediocanellata_ with the _Botriocephalus_, which are cestodes 213

peculiar to vegetable-feeders. As a feeder on vegetable diet he also

harbours vesicular agamous cestodes, which are only found in him as

passengers.

The _Tænia serrata_ of the dog lives at first as a passenger in the

peritoneum of the hare and the rabbit; and every one knows how

greedily the dogs eat the viscera of these animals.

The cat entertains another kind of tænia, and, as we may easily

suppose, in its young state it lives as a passenger in the mouse or

the rat. Who then has traced out for it this itinerary, and pointed

out the way, the only one by which the parasite can hope to take

possession of its proper abode? Evidently it is neither the tape-worm

nor the cat. The plan for all these various species is marked out

beforehand, and each animal as soon as it is born knows it without

being taught.

A Danish naturalist, Mons. H. Krabbe, has just finished a special work

on cestode worms of the genus _Tænia_, and he remarks that there is no

class in which these worms are so abundant as in that of birds. It is

among the rapacious and carnivorous birds of this class that they are

less abundant. Among mammals, the carnivora possess the greater

number. This fact, as M. Krabbe remarks very rightly, seems to

indicate that the cestodes of birds especially employ the inferior

aquatic animals as their vehicles when in their incomplete state.

Let us consider the solitary worm of man (_Tænia solium_), it will

enable us to understand all the others. Known by the name of tænia, or

solitary worm, it is, like all the cestodes, a marvellous association

of mothers and daughters, which are developed and vegetate in a 214

peaceable community. Each segment is a complete being, which encloses

within itself an entire and very complicated apparatus for the

fabrication of eggs.

We give (Figs. 51 and 52) the representation of a solitary worm,

peculiar to man, of the natural size; and at the side the scolex,

usually called the head, slightly magnified.

[Illustration: Fig. 51.--_Tænia solium_, or solitary worm; _a_, head,

or scolex; _b_, tape formed of many individuals, the last of which,

completely sexual, separate under the name of _proglottides_, and

represent the adult and complete animal. Each solitary worm is a

colony.]

[Illustration: Fig. 52.--_a_, Rostellum; _b_, crown of hooks; _c_ _c_,

suckers; 1, scolex of the tænia solium; 2, hooks expanded; _a_, heel

of the hook.]

Under its first vesicular form the solitary worm is planted in a 215

provisional soil. After this it is transplanted into a richer soil,

where it flowers and throws out its numerous seeds. It comes to us

from the flesh of the pig, in which there lived vesicular worms, of

the size of a hazel-nut. The muscles are sometimes full of them, and

the pig is then said to be "measly." The ancients noticed that the

sucking-pig never takes this disease; and as _Sus scropha_ is the

name of the pig, the term scrophula has the same origin as the

specific name proposed by Linnæus.

The measles in pork have been attributed to damp, to feeding on

acorns, to hereditary causes, to contagion, even to injured corn and

mouldy bread. All these theories we find in pathological treatises.

The only true cause, however, is the introduction of the eggs of the

_Tænia solium_ into the intestines. If we wish to prevent this

infection, we must not permit the animal to eat man's excrements, nor

to drink water in which substances that have become decomposed on a

dung-heap have been allowed to remain.

The cysticercus of the pig, when introduced into man, becomes a tænia

with as great certainty as the seed of a carrot will produce this

plant if sowed in suitable soil. The observation had been for a long

time made without any explanation being given, that this parasite

especially shows itself among pork butchers and cooks. This is because

these persons, more frequently than others, handle raw pork. The same

observation has been made respecting children who have made use of the

gravy of raw meat. Minced raw meat (_conserve de Damas_) has been

prescribed with success in chronic diarrhoea. The tape-worm has

often been known to make its appearance after this treatment, as 216

may well be supposed. Tænia helminthosis is constant and general in

Abyssinia, and they there commonly eat raw beef. Those who do not eat

meat, as the monks of certain orders there, who live only on fish and

flour, never have the tænia. Ruppell and many others have noticed this

fact. Mons. Küchenmeister says that at Nordhausen, in the Hartz, as

well as throughout all Thuringia, measles are very prevalent among

pigs; and as the people are in the habit of eating minced pork, both

raw and cooked, spread on bread for breakfast, this country may be

looked upon as the Abyssinia of the north.

The doctor at Zittau caused a man who was condemned to death, to take,

seventy-two hours before his execution, some cellular cysticerci from

a measled pig; and he found in the duodenum of the man four young

tæniæ, and six others in the water in which they had washed the

intestines. The latter had no hooks, but those of the former had some

in every respect similar to those of the _Tænia solium_.

We have ourselves caused a pig to swallow eggs of the tænia, and have

given it the measles. Messrs. Küchenmeister and Haubner, who were

ordered by the government of Saxony to make some experiments, also

caused three pigs to swallow eggs of the _Tænia solium_, and two of

these were affected with measles. A piece of flesh, weighing 4-1/2

drams, contained 133 cysticerci, which amounts, for 22 German lbs., to

88,000 cysticerci.

The use of raw pork will produce tæniæ more readily than raw beef. Dr.

Mesbach has given the following instance in support of this fact. At

Dresden, a father and his children regularly ate, at their second 217

breakfast, raw beef, but one day they took pork instead, and eight

weeks afterward one of the children, when in the bath, voided two ells

of _Tænia solium_.

The etiology and prophylaxis of the solitary worm, that is to say, its

mode of introduction, and the means of protecting ourselves from it,

are clearly indicated. It is sufficient to introduce one of these

vesicles into the stomach in order to have the tape-worm. The

experiment has been made: young men have ventured, in the interests of

science, to swallow some, and have ascertained how many days were

required for the parasite to be sufficiently complete to give off

segments with the feces.

These vesicles in pork come from the eggs which the tænia has

scattered in its passage, and if the pig comes by chance in contact

with the fecal matter of a person infested by one of these worms, it

is soon infested and becomes what is called measled; in this fecal

matter there are either free eggs which have been evacuated by the

worm, or else fragments, known long since under the name of

cucumerinæ, which are full of eggs.

These fragments of tænia, which I have proposed to name proglottides,

and which are nothing else than the worm in all its sexual maturity,

are still living and wriggling at the moment of their evacuation, or

else they are dead and often completely dried; but in either case,

they are full of eggs. Each egg is surrounded by membranes and shells,

which effectually protect it against all dangerous contact.

A fragment of the mature tænia, thus filled with eggs, when introduced

into the stomach of the pig, is rapidly digested, and the eggs are set

at liberty. These lose their shells by the action of the gastric 218

juice, and there issues an embryo singularly armed. As we have before

said, it carries in front two stylets in the axis of the body, and on

the right and left sides two other stylets curved at the end, which

act like fins. These embryos bore into the tissues as the mole burrows

into the soil. The middle stylets are pushed forward like the snout of

the insectivore, and the two lateral stylets act like the limbs,

taking hold of the tissues and forcing the head forwards. In this

manner the embryos perforate the walls of the digestive tube.

An egg of the _Tænia solium_ may be swallowed by a man instead of

passing into the stomach of the pig. It is hatched in his stomach

precisely in the same manner, and the embryo takes up its lodging in

some enclosed cavity. Some have been found in the eye-ball, in the

lobes of the brain, in the heart, or in the muscles. We have lately

read an account of the effects produced by one of these wandering

worms, on a man who died after suffering from a peculiar disturbance

of the mind. Two spirits seemed to haunt and speak to him, the one a

German, the other a Pole. Filthy images were called up before his

imagination. At the post-mortem examination, cysticerci were found to

occupy the sella turcica, near the commissure of the optic nerves. One

of these was alive, the others were calcified. Two others in a similar

condition occupied a lobe of the brain.

Man harbours not only the _Tænia solium_, but another species very

similar, which naturalists have only learned to distinguish from it

during the last few years, the _Tænia medio-canellata_. We give a

magnified representation of the scolex, that is to say, of the head of

this worm, which has no crown of hooks in the middle of its four 219

suckers.

[Illustration: Fig. 53.--Tænia mediocanellata.]

This solitary worm is introduced by means of beef, and the cysticercus,

during its abode in the cow, manifests already the peculiar

characteristics which enable us to recognize the species, that is to

say, no crown of hooks, but four suckers, and in the middle of them,

some blotches of pigment. Leuckart fed a calf with eggs of this tænia,

and at the end of seventeen days, the animal died of acute miliary

tuberculosis, produced by the great abundance of cysticerci. This

second species, which had been always confounded with the preceding,

and which is nevertheless the more common, has therefore a different

origin from the _Tænia solium_. Observations made quite recently in

the north of Africa demonstrate this. Great difficulty had sometimes

been felt in explaining the presence of the tænia in persons who had

not eaten pork. This embarrassment arose from the confusion of the two

species, and this confusion is the more easy as the head of the colony

must necessarily be found in order to distinguish them.

Scharlau, at Stettin, found tæniæ in seven children who had been fed,

on account of anæmia, with raw meat. The tæniæ were those of this

species. We have ourselves found them in children to whom the use of

raw meat had been prescribed.

We do not think it necessary to speak here of a third species of tænia

(_T. nana_), which also lives at our expense, but which has been 220

hitherto found only in Egypt.

We know perfectly well the itinerary of the _Tænia serrata_ of the

dog, which is so abundant, that there are few of these animals that do

not enclose some and even many of them. There are few except lapdogs

which do not harbour them. We can easily assign the reason. Every

tænia, like every animal, has its eggs; each plant has its seeds.

These eggs are laid by the mother in the most favourable condition for

the development of her progeny. The dog deposits its dung on the grass

rather than in any other spot, because the eggs of its tænia, which

are destined to the rabbits or hares, will have greater chance of

arriving at their destination than if they were exposed on the bare

earth, or in the water. Their prodigious number is calculated

according to the chances of their arriving safely. The egg, when

introduced into the stomach of the rabbit, is rapidly hatched in this

organ under the action of the gastric juice, and the embryo which is

produced from it seeks its hiding-place in the midst of the tissues

which surround it; it bores into them, and establishes itself in the

folds of the peritoneum. Then, once in its resting-place, it

barricades itself, and waits patiently for an opportunity of

introducing itself into the stomach of the dog.

This microscopic embryo is armed with six hooks, like embryos of all

the cestodes; it employs them with much dexterity to pierce the walls

of the organs, and to hollow out a space for itself in the substance

of the tissues. Shut up in its hiding-place, membranes form around for

its protection; its six hooks, having become useless, wither; other 221

hooks in the form of a crown appear by the side of four rounded

projections, the future suckers; and, sheathed in a large vesicle full

of a limpid fluid, it waits patiently for the moment when it will find

a place in the stomach of a dog. If good fortune awaits it, it will

wake up, some fine day, in the stomach of the animal which has eaten

the rabbit, its former home, and a new life will commence for it. The

organs in which it was imprisoned are digested, it gets rid of all its

swaddling-clothes, unrolls itself, separates from the vesicle which

has protected it hitherto, and penetrates into the intestine; there,

immersed in the food of its host, it grows with extreme rapidity, and

assumes the form of a ribbon or tape. The ends of this tape are

successively matured, detach themselves, and become the complete

worms, full of eggs, which are evacuated with the feces; scarcely have

they made their appearance in the open air before they burst and

scatter their eggs.

He whose scientific curiosity is sharpened, has only to watch the dung

of the dog at the moment of its evacuation to distinguish on its

surface worms of a milky-white colour, contracting like leeches, which

are the true _Tænia serrata_ in its adult state. Experiments made

on this species have given sanction to what I had said respecting the

cestodes.

The tænia, under the name of _Cysticercus cellulosus_, lives in

the folds of the peritoneum of the rabbit and the hare, and passes

directly from the rabbit to the dog to become complete.

It is very curious that the fox, so nearly allied to the dog in

appearance, and which also eats rabbits, never has the _Tænia

serrata_, but this animal nourishes other worms.

It was with these cysticerci that I made experiments on four dogs, 222

which I took with me to Paris, in order to convince those who could

not believe in the migration of parasites. It was this species that I

gave also to the dogs which served as a demonstration at Paris at the

course of lectures given by Mons. Lacaze Duthiers.

Some years ago, while making a post-mortem examination, at the Museum

of Paris, of some young dogs which I had previously infected with

_Tænia serrata_ at Louvain, there were found by the side of these some

_Tæniæ cucumerinæ_. These dogs had taken nothing but milk and

cysticerci! Whence came these _Tæniæ cucumerinæ_? I knew not, and I

frankly owned it to the members of the Commission who proposed the

question to me. This however did not prevent my being greatly puzzled

with the presence of this worm of whose origin I had no idea. Now we

know whence they came. An acaris, the Trichodectes, lives in the hair

of young dogs and harbours the scolex of this cestode. The dog, by

licking its own hair, grows infested, like the horse, which in a

similar manner introduces the gad-fly, and although it has taken no

other nourishment, harbours its own epizoaria.

The name of _Cysticercus tenuicollis_ has been given to a vesicular

worm which inhabits the peritoneum of the ox, the goat, the sheep,

&c., and which turns to a tænia in the digestive tube of the dog.

Mons. Baillet has made the principal experiments on this

transmigration. The itinerary of another cestode worm, the _Coenurus_

of the sheep, is to pass through the sheep in order to reach the wolf

or the dog. This worm has only lately been recognized in its tænoïd

form; it has, on the contrary, been long known under the name of

_Coenurus cerebralis_; this develops itself on the brain of the 223

sheep, and occasions the disease known by the name of "gid." This

disease may be produced artificially. The sheep which swallows the

eggs of this tænia shows the first symptoms of it towards the

seventeenth day. If we kill it at this time, we find on the surface of

the brain, either at the base or the summit, or sometimes between the

hemispheres and the cerebellum, one or more white vesicles of the size

of a pea, and on which no traces of buds are yet to be seen. This

vesicle, of a milky-white colour, and filled with liquid, is the

scolex. Near these vesicles are to be seen some very irregular yellow

furrows, like tubes abandoned by some tubicolar annelid; this is the

gallery through which the vesicular worm has proceeded to the place

where it has been found.

[Illustration: Fig. 54.--Coenurus of the sheep. 1, the enclosed

scolex; 2, Hydatic vesicle, with the scolices in their place within

it.]

A fortnight later, that is to say, about the thirty-second day, the

coenurus is as large as a small nut, and one can see with the naked

eye some small nebulous corpuscles, separate from each other, of the

same form and size; these are the buds or scolices which have risen

up, but which, as yet, have neither hooks nor suckers.

We give the representation of one of these vesicles, on the internal

walls of which young scolices have been developed; this is nearly of

the natural size. Fig. 2, _a_, _a_, shows these scolices of nearly

the natural size. Fig. 1 represents an isolated and magnified scolex; 224

A, shows the segments of the future proglottides; D, the suckers; C,

the hooks; H, the vesicle which contains them.

Eggs of the same tænia have been given to sheep at Copenhagen and at

Giessen, and Messrs. Eschricht and R. Leuckart have obtained the same

result as we had at Louvain. On the fifteenth or sixteenth day the

first symptoms of "gid" declared themselves. At about the

thirty-eighth day the crown of hooks appeared, the suckers were

formed, and the whole head of the scolex was sketched out. All these

heads can leave or enter the sheath at the will of the animal. It is

truly a polycephalous animal when the scolices are expanded. This worm

continues to grow for a long time in the cranial cavity, and produces

by its presence the gravest results. The sheep necessarily dies at

last, unless we remove the parasite by means of the trepan.

The coenurus, at this point of development, swallowed by a dog,

undergoes great changes in a few hours. The proscolex, or large

vesicle, withers; the different scolices unsheath their cephalic

extremity, become free, penetrate into the intestine with the food,

and attach themselves to its walls, so as to form as many colonies of

tænia as there are distinct heads. A dog which has swallowed a single

coenurus may therefore contain a considerable number of tæniæ.

The development of this worm proceeds very rapidly, and it only

requires three or four weeks to attain many feet in length. The

organization of this worm, in the state of strobila and of proglottis,

is in every respect like that of the _Tænia serrata_; we have

even endeavoured in vain to distinguish these worms from each other 225

by their hooks. The wolf or the dog follows the flock of sheep,

scatters the proglottides or the eggs in their way, and the sheep,

browsing on the grass with the eggs attached, become infested with

their most dangerous enemy.

To arrest this disease, only one thing is necessary, to destroy by

fire the head of every sheep attacked by the "gid." The rest of the

animal may be eaten without danger.

Pouchet did not succeed in giving sheep the "gid" at first, for the

very simple reason that he employed the eggs of the _Tænia serrata_,

instead of those of the _Tænia coenurus_; he had confounded the two

species. The coenurus of the sheep is a true calamity when it spreads

in a country. The animal attacked by it is lost, and the mischief may

be indefinitely propagated by giving as food to dogs the head of the

sick animal, with thousands of young tæniæ enclosed within each.

There exists a singular cestode which bears the name of

_Echinococcus_. We give a figure of the echinococcus of the pig,

slightly magnified, and an isolated scolex (Figs. 55 and 56). In its

first form it is composed of closed sacs, which grow to the size of a

nut, and sometimes to that of an orange. It usually lodges in the

liver of the pig, but establishes itself also in man. We have been

assured that part of the population of Iceland have been attacked by

it. The abundance of this parasite in that country is attributed to

the want of cleanliness, and the number of dogs that they keep around

them. The echinococcus becomes a tænia in this animal. It scatters the

eggs with its dung, leaving them directly or indirectly on plants

which the Icelanders eat; for they gather for food certain mosses, 226

sorrel, cochlearia, dandelion, &c., from the midst of the plains in

which live flocks of sheep guarded by dogs. The eggs are scattered

everywhere on plants or in the water.

[Illustration: Fig. 55.--Isolated scolex of the _Tænia echinococcus_

from the pig.]

[Illustration: Fig. 56.--_Tænia echinococcus_, from the pig.]

Leuckart has made some very interesting experiments on the

echinococci. In Fig. 57 is shown a tænia which proceeds from an

echinococcus.

[Illustration: Fig. 57.--_Tænia echinococcus_, from the dog.]

[Illustration: Fig. 58.--Bothriocephalus latus. _a_, scolex, _b_, the

proglottides, _c_, the sexual organs.]

There is yet another tape-worm harboured by man, the _Tænia lata_,

better known under the name of Bothriocephalus. We give in Figs. 58, 227

59, and 60 representations of this worm in the state of a colony, also

the scolex or head separately, and an egg. Its history is very

curious, especially with reference to its geographical distribution.

It is only found in Russia, Poland, and Switzerland, and the limits 228

of the places which it inhabits are perfectly defined. Siebold, during

his stay at Königsberg, could determine from the nature of the worms,

whether the patient who consulted him lived on one side or the other

of the Vistula.

[Illustration: Fig. 59.--Bothriocephalus latus, scolex.]

[Illustration: Fig. 60.--Bothriocephalus latus, egg.]

A Russian naturalist, Dr. Koch, thoroughly studied this interesting

worm and its evolution. He says that this cestode is rare at Moscow,

while at St. Petersburg, Riga, or Dorpat it is common. If this be

really the case, it must doubtless be attributed to the fact that in

one place the inhabitants drink spring water, and in the other water

from the river.

A very curious circumstance is the actual rarity of the Bothriocephalus

among the inhabitants of the shores of the Lake of Geneva, though

formerly it was very common there. This diminution, if we may not call

it disappearance, is due to the change which has been made in the

construction of water-closets, all of which formerly emptied

themselves into the lake, so that the embryos were hatched in the

water, and persons were infested by them through drinking it. At

present the refuse of the towns is carefully collected for the purpose

of manuring the land. This is the result of the advice of Mons. de

Candolle, half a century ago; for this naturalist clearly understood

how great was the loss to agriculture from the neglect of this

fertilizing agent.

The itinerary of this tape-worm is simple. It passes from man to the

water under the form of an egg, or of a proglottis; and from the water

to man in the shape of a ciliated embryo. In this manner it is

introduced with the water that is drunk. The Bothriocephalus, like

other cestodes, is free at the commencement and the end of its life: 229

at the beginning, in order to penetrate into its host; at the end, to

scatter its eggs.

Messrs. Sommer and Landois published, in 1872, an anatomical description

of the sexual organs of the _Bothriocephalus latus_, of such

completeness, that it will be long before any one will again take up

this subject, which had so much occupied helminthologists ever since

the celebrated work of Eschricht. This memoir is illustrated by superb

engravings, which represent these organs under every aspect. Dr.

Böttcher, of Dorpat, found in the small intestine of a woman, who died

of peritonitis, at least a hundred Bothriocephali. They were but

slightly developed, though there were some in a sexual state.

The largest tænia, though not the longest, is the _Tænia magna_, from

the _Rhinoceros_, described by Marie; it is, no doubt, the same to

which the name of _gigantea_ was given by Peters. The learned director

of the Museum of Berlin gave me a fine specimen of it eighteen years

ago. The generic name of _Plagiotænia_ has been proposed for this worm.

Almost all birds nourish large and beautiful tæniæ, but they must be

studied immediately after the death of their host. They often change

their form entirely at the end of a few hours.

Woodcocks and snipes always have their intestines stuffed full of

tæniæ and the eggs of these worms. Every bird contains them by

thousands. Fortunately we cannot be infested with the tænia of the

snipe and the woodcock.

Fig. 61 represents the scolex of the _Tænia variabilis_ of the snipe, 230

and Fig. 62, by its side, shows the crown of hooks more highly

magnified. We have made these drawings from worms collected from

snipes some instants after their death. We close this chapter on the

cestodes with the plate (Fig. 63) of a Tetrarhynchus which is usually

found in the plaice. The perfect tetrarhynchi, that is to say, those

that are adult and sexual, inhabit the intestines of voracious fishes,

especially of the squalidæ.

[Illustration: Fig. 61.--Tænia variabilis from the snipe.]

[Illustration: Fig. 62.--Tænia variabilis from the snipe. (Crown of

hooks.)]

[Illustration: Fig. 63.--Tetrarhynchus appendiculatus from the plaice.]

There are other worms which migrate, and even some articulate animals;

but their modifications of form are much fewer than in the preceding,

and their changes are generally restricted to simple metamorphoses. We

will place at the head of this chapter the Linguatulæ, which have so

perplexed naturalists.

We sometimes find in the nasal fossæ of the dog and the horse a worm

resembling a leech, with a body completely etiolated, which lives

there entirely as a parasite, and whose history has only been known 231

for a few years. Chabert discovered the first species of this group in

1787 in the frontal sinus of the horse and the dog. It had been named

_Tænia lanceolata_. All naturalists, Cuvier included, placed this

animal among intestinal worms, under the name of _Linguatula_ or

_Pentastoma_. The latter name had been given to it, because they

mistook the hooks for mouths.

We have shown, from the embryos, in 1848, that the Linguatulæ, instead

of being worms, are articulate animals, more allied to the lerneans or

acaridæ than to the helmintha. These observations, though received at

first with much hesitation, were fully confirmed afterwards,

especially by the learned researches of Leuckart. The linguatulæ have

a very long body, sometimes rounded, in other cases compressed, with a

mouth surrounded by four strong hooks, regularly disposed in a

semicircle. They have often been found in the lungs of serpents, in

certain birds, and in many mammals. A linguatula was also seen by

Bilharz at Cairo, in the liver of a negro, and they have been observed

in the hospitals of Dresden and Vienna.

It is to be presumed that this dreadful parasite has been introduced

into man by means of the flesh of the goat, and perhaps of the rabbit.

Linguatulæ are found in their primary agamous form, in open cavities

like the nasal fossæ. Leuckart was the first to show that the

linguatulæ, which lived at first encysted in the peritoneum of the

rabbit, completed their evolution and became perfect in the nasal

fossæ of the dog. The _Linguatula serrata_ (Fig. 65), which lives

primarily in the goat, the guinea-pig, the hare, the rabbit, &c., 232

is found accidentally in man, and perfect in certain mammals. Examples

have been given of sick persons being completely cured by the

evacuation of worms from the nostrils; these worms were, doubtless,

linguatulæ. Fulvius Angelianus and Vincentius Alsarius speak of a

young man who had suffered for a long time from head-ache, and who

passed a worm from his nostrils. It was as long as the middle finger.

There is little doubt that this was the _Linguatula tænioïdes_. These

parasites may perhaps sometimes lose their way in their peregrinations.

Some years ago a lioness died of peritonitis at Schönbrunn, and, after

death, the liver, the spleen, and other organs were found to be filled

with encysted linguatulæ.

[Illustration: Fig. 64.--Isolated hook of Linguatula.]

[Illustration: Fig. 65.--Linguatula magnified six times. Four hooks

are seen around the mouth in front. _c_, the anus.]

The nematode worms are long and rounded, like the ordinary ascarides

of infants, which take up their abode in all the organs of animals of

the various classes of the animal kingdom. About a thousand varieties

are known, varying in length from a few millimètres to forty or 233

fifty centimètres.

They are not all parasites, as has been thought, since some are found

in the sea, and others in damp earth, in putrid matter, and even on

plants and their seeds. The migrations of nematodes are subjects of

great interest. Their changes of form are usually not very

considerable; but the modifications in their sexual apparatus, whether

in the same individual, or in the succeeding generations, are very

curious.

When we consider the numerous encysted and agamous nematodes, which

are found in the different orders of mammalia, birds, reptiles,

batrachians, and fishes, there is little doubt that all these beings

are only migratory parasites, which pass together with their hosts

into the animal to which they are destined. They are found, like

ascarides, in animals of all classes. Some are to be met with in all

the organs--the brain, the eye, the muscles, the heart, the lungs, the

tracheal artery, the frontal sinus, the digestive tube, the skin, and

even in the blood. Sometimes the two sexes live under the same

conditions; sometimes the male is dependent on its female, or else one

generation is parasitical, and the next is independent. There is a

great diversity with respect to development. Some nematodes, like

trichinæ, are developed so rapidly, that the embryos are already

perfect in the egg before it has quitted its mother. Others, like the

ascarides lumbricoides, lay eggs, in which the embryos do not appear

till several weeks or many months after they have been laid. Between

these two extremes we find all the intermediate degrees.

Diezing, who has done more for systematic helminthology than any 234

other naturalist, brought together, under the name of _Agamonema_, all

the migratory agamous nematodes which wait for the opportunity of

entering their final host. Diezing had kept himself quite independent

of the discussion by fixing his attention exclusively on form, without

taking account of migration and digenesis. One of these agamonemata,

lodged in the midst of a pediculated cyst on the vagina of a bat (the

little horse-shoe), was probably a worm that has lost its way; if not,

we must admit that these mammals become the prey of some carnivorous

animal. But what carnivore can habitually feed on the cheiroptera?

There are but few fishes, either in fresh or salt water, which do not

enclose in the folds of their peritoneum, especially round the liver,

cysts full of these agamonemata.

We see in some of the nematodes examples of migration which are quite

peculiar to them. Some of these worms are always free, others free at

one part of their life only, others migrate from one animal to

another; others again from one organ to another. The _Ascaris

nigro-venosa_ of the frog lives sometimes in the lungs, at others in

the rectum or quite out of the body in damp earth. The _Filaria

attenuata_ lives in the rook (_Corvus frugilegus_), and it is said

that it becomes sexual in the intestines of the same bird.

These worms are usually very tenacious of life; many of them can, it

is said, be dried for weeks, months, or years together, and return to

life as soon as their organs are moistened. Their eggs resist even the

action of alcohol and the most active chemical agents, and eggs that

had been prepared for the microscope, and had served for many years 235

the purposes of study, have been known to produce young ones as if

they had been just laid.

_Natura non facit saltus_ is especially true as to the division of

sexes among the nematodes. Between the true hermaphrodites and the

true dioecious worms are found species in which the males gradually

dwindle and become dependent on the female; this is to be seen in the

_Sphoerulariæ_, among which the male is only an appendage to the

female sex. We find here full evidence of the fact that the female is

more important than the male, with regard to the preservation of the

species. In some species the sexes differ but little, in others, the

sexual differences become greater, and the male is only one third of

the length of the female; but in some of them the disproportion is

greater still. At the same time, we see nematodes whose males are

attached to the females, so as only to form a single individual; in

other cases, the male seems to disappear to such an extent, that we

find nothing but the male organ in the female; indeed, there are

instances of male worms, which, without changing their form, occupy

the cavity of the matrix and, like the lernean crustaceans, are

parasites of their females. The _Trichosomum crassicauda_ is an

instance of this kind.

Arrangements which would not have been suspected beforehand, are every

day revealed, with respect to the conservation of species. We have

recently learned from the works of Messrs. Malmgren and Ehlers, and

later still, from those of Claparède, that in the same species we may

find different males, producing different offspring. Messrs. Malmgren

and Ehlers have opened this question by their persevering researches, 236

and Mons. Claparède expected to invalidate the results obtained by

them by establishing himself at Naples, in order to devote himself to

a new series of investigations. Contrary to his expectations, he

arrived at the same conclusions, and announced that a nereid

possesses, in one and the same species, two kinds of males and two

sorts of females, and that these males differ from each other, not

only in their manner of life but in their age, in the mode of

formation of the spermatozoïds as well as in the form; that the

females differ no less from each other than the males, and that each

form is intended to provide, in its own manner, for the dissemination

of the eggs.

We see this realized in annelid worms known by the name of

_Heteronereidæ_. Certain individuals of small size live on the surface

of the water; others, evidently much larger, live at the bottom of the

sea and behave quite differently. The eggs and the spermatozoïds

proceeding from these two forms differ sensibly from one another, and

the difference of form corresponds with that of origin.

We see thus among some of them different males; among others different

females: then eggs and spermatozoïds equally different in one and the

same animal species.

A curious insect, the _Termes lucifuga_, appears also to distinguish

itself by two sorts of males and females, which even take to flight at

different periods. Great sagacity was required to reveal these strange

facts. Mons. Lespes has had the courage to devote himself to these

observations.

We see that all means are good that are for the preservation of the 237

species, but who would have suspected that in a single animal there

would be found two males by the side of two females, neither of which

resembles the other, and besides these, two kind of eggs and

spermatozoïds! How great would be our astonishment were we to see two

sorts of cocks, two kinds of hens, and two sorts of eggs produced by

the same mother, and hatched at the same time!

Professor Ercolani bred in damp earth certain parasitical nematodes,

kept them alive, saw them reproduce, and was even able to obtain

several generations of them. These nematodes were the _Strongylus

filaria_ from the lungs of the goat, the _Strongylus armatus_ from the

intestines of the horse, the _Ascaris inflexa_, and the _Ascaris

vesicularis_ from the fowl, and the _Oxyuris incurvata_ from the

horse. The first three, whether they are born in damp earth, or in the

midst of organs in which they habitually lodge, have the same external

characters; nothing is remarked in them except a greater activity in

their reproduction.

The _Strongylus armatus_, when born at liberty, appears no longer to

have hooks at the mouth like those worms which live in the intestines.

Mons. Ercolani has also remarked that these worms, when they become

free, are ovo-viviparous, though they were before oviparous.

There are many of these nematodes which are true parasites of man, and

although certain of these are as much dreaded as the plague or the

cholera, we are far from knowing all their history, and especially the

manner in which they are introduced.

A young naturalist, Dr. O. Bütschli, has lately made a good _résumé_ 238

of the state of our present knowledge of parasitical and wandering

nematodes.

The Sclerostomata are distinguished by their mouth being surrounded by

a horny armature. The river perch usually gives lodging to a

viviparous nematode, the _Cucullanus elegans_, on the development

of which a special work has been published. The young ones are

provided with a perforating stylet, and penetrate into the bodies of

small aquatic crustaceans, called cyclops. When they have obtained

entrance into this living lodging, they bore through the walls of the

intestines and shut themselves up in the perigastric cavity. The

cyclops being pursued by the young perch, are swallowed with their

guest, and the latter is set free in the midst of the stomach, where

it passes through its sexual evolution.

Leuckart saw in his aquarium young Cucullani penetrate into the bodies

of the cyclops. These crustaceans are therefore the vehicle of these

nematodes. Another nematode worm, the _Dochmius trigonocephalus_,

lives at liberty while young, but seeks for an asylum in the dog in

its old age. The _Sclerostomum equinum_ causes aneurisms in the horse,

which manifest themselves by colic. A hundred of these worms have been

found in the same horse. The _Sclerostomum pinguicola_ is very common

in the pig in the United States. This is the _Stephanurus dentatus_ of

Diezing, noticed by Natterer in Chinese pigs in Brazil. Cobbold

notices the same worm as living in the pig in Australia; they have

been also found in Germany.

The _Strongyli_ are round, cylindrical worms, with bodies sometimes

entirely red, which inhabit different organs in mammals and birds. 239

A very remarkable species, the _Strongylus gigas_ (Fig. 66), exists in

the kidneys of the horse and the dog, and sometimes in man. It partly

destroys this organ, and has been seen a mètre in length. The

_Strongylus commutatus_ often lives in great abundance in the lungs of

the hare, and the _Strongylus filaria_ in the lungs of the sheep,

occasionally in such great numbers that their presence produces

pneumonia.

[Illustration: Fig. 66.--Strongylus gigas.--1, female, showing _a_,

the mouth; _b_. the intestine; _c_, genital pore; _d_, anus. 2,

cephalic extremity of the male; _a_, mouth; _b_, oesophagus. 3, caudal

extremity of the male; _a_, cup; _b_, penis. 4, egg.]

Porpoises generally have strongyli in their lungs and their bronchia,

and they are seen by thousands in the sinus of the Eustachian tube. 240

We collected a large bottle full from a single porpoise around its

internal ear. When we consider the prodigious number of these

creatures, may we not suppose that they are able to multiply in the

organs which they occupy, as well as migrate to infest other

individuals.

Different generic and specific names have been given to these

Strongyli. A round worm found in the intestines of the dog, the

_Strongylus trigonocephalus_, lives at first in damp earth or mud

like the rhabdites in general; it then passes into the dog, and there

becomes a sexual Strongylus. It is possible that there are others in

the same category.

[Illustration: Fig. 67.--Ascaris lumbricoides.--1, complete worm, 2,

head, 3, tail of the male, 4, middle of the body of female.]

The _Ascaris lumbricoides_ is a large round worm which attains the

size of a quill pen, and which is commonly found in the stomach or the

lesser intestines of children when in good health. Aristotle was

acquainted with it. It has been observed throughout Europe, in Central

Africa, in Brazil, and Australia. The same species lives in the

intestines of the pig; but the _Ascaris megalocephalus_, which is

usually found in the horse, is of a different species.

The _Ascaris acus_ of the pike lives at first in a common white 241

fish, the _Leuciscus alburnus_, and passes with this fish, which

serves it as a vehicle, into its final host.

Another common nematode, the _Oxyurus vermicularis_ (Fig. 69), a

parasite of man, is a small worm of the size of a fine pin, which

often multiplies in the rectum of children, causing intolerable

itching. It is by means of their microscopic eggs that they penetrate

into the system; these are hatched in the stomach, and are completely

developed at the end of eight or ten days. They pass from the anus in

great numbers.

[Illustration: Fig. 68.--Trichocephalus of man.--1, female, _a_,

cephalic extremity, _b_, caudal extremity and anus, _c_, _d_,

digestive tube and ovary, _e_, orifice of sexual apparatus. 2,

isolated egg. 3, male, _a_, cephalic extremity, _b_, anus, _c_,

digestive tube, _d_, spicula or penis, _e_, sheath into which it is

withdrawn.]

[Illustration: Fig. 69.--Oxyurus vermicularis.--1, male of natural

size, 2, female, id., 3, cephalic extremity, magnified.]

The brood of worms from the eggs of the _Ascaris megalocephala_

of the horse live in freedom, and go through all their phases until

their sexual development separately; there are males and females. The

generation which descends from these is distinguished by being of a 242

much smaller size.

The name of _Trichocephalus_ has been given to nematodes which have

the cephalic extremity very thin, and ending in such a fine point that

it is difficult to discover the mouth. The Trichocephalus of man (Fig.

68) is a curious nematode, which was discovered by a student at

Göttingen, in 1761. It is usually found in the cæcum, in which more

than a thousand have been met with together. The female is from 40 to

50 millimètres long, the male about 37 millimètres. A female

_Trichocephalus affinis_ having laid her eggs in an aquarium, the

whole of the contents were introduced into the stomach of a lamb,

seven months afterwards, and the walls of its intestines became

infested with trichocephali.

No animal at any time has attracted so much attention as that little

worm which lives in flesh, rolled up; it is about the size of a millet

seed, and was found by chance in the dissecting-room of a London

hospital, some forty years ago. The plague and the cholera did not

inspire so great fear, and this fright had almost passed from Germany

throughout the rest of Europe. We were not among those who wished to

take measures at all hazards against the invasion of this worm, since

nothing induced us to believe that more trichinæ existed then in

Belgium than in ordinary times. These measures would have produced no

other effect than uselessly to disturb the minds of the public.

Trichiniasis, which was the name given to the disease caused by these

worms, reminds us of tarantism, that is to say, the effects produced

by the bite of the tarantula. Mons. Ozanam wrote an interesting work

on this subject, in which he said that nervous tarantism existed 243

during two centuries in Europe, as an epidemic malady. According to

him, there prevails at present in the province of Tigre, in Abyssinia,

a sort of chorea, or endemic musicomania, which has a great analogy

with tarantism; it is the "Tigretier." Nothing but music and dancing

can have any beneficial effect during the crisis; but these means

would evidently be inefficacious in trichiniasis.

[Illustration: Fig. 70.--Trichina.]

[Illustration: Fig. 71.--Trichina, rolled up in a muscle.]

The Trichina is a nematode worm, and not an insect, as it was at first

called. Let us imagine an extremely slender pin, such as entomologists

employ to fasten the smallest insects, rolled upon itself in a spiral

form so as to lodge in a cavity hollowed out in the midst of the

muscles, in a space not larger than a grain of millet. These trichinæ 244

of the muscles can be discerned by the naked eye. But before we enter

on a particular description (and they are now known in their minutest

details), let us notice what were the circumstances which led to their

attracting so much attention.

It was in 1832; a demonstrator of a course of anatomy at Guy's

Hospital in London, Mr. J. Hilton, found in the flesh of a man

sixty-six years of age, who died of a cancer, a great number of little

white bodies which he took for vesicular worms. The scalpel, during

the dissection of the muscles, met with granulations which blunted the

edge of the instrument. Astonished to find in the flesh hard

corpuscules which the instrument divided with difficulty, he removed

some of them, examined them attentively, but, no doubt, he was not

sufficiently acquainted with helminthology to understand their true

nature. He referred to Professor R. Owen, the celebrated naturalist of

the British Museum, who recognized them as new worms, and gave them

the name of _Trichina_, because they are as thin as a hair; he added

the specific name of _spiralis_ on account of the manner in which they

were rolled up in their cyst. _Trichina spiralis_ is therefore the

name of this animal.

Some naturalists, at that time, believed that the filaments of the

fecundating fluid of the male were parasitical worms, such as are

found in other liquids; and these filaments which were designated by

the name of spermatozoïds (the animalculæ of the older naturalists),

were considered as beings having a certain affinity with trichinæ. The

trichinæ were the intermediate state between these filaments of the

fecundating fluid and worms properly so called. It is now known with

certainty that these filamentary bodies are no more animals than the 245

globules of blood, and that all that was thought to have been observed

of their organization was nothing but pure fancy.

The trichinæ, which are now completely known in the minutest details

of organization and manner of life, have a distinct mouth, and they

have a complete digestive tube with an orifice at each end of the

body, like all worms in the form of a thread, which, for this reason,

are called by naturalists _Nematodes_ as opposed to _Cestodes_ (in the

form of a ribbon or tape). Besides this nutritive apparatus, trichinæ,

like nematodes in general, have the sexes divided into two distinct

individuals, so that there are males and females, which can be easily

distinguished from each other by the size and form of the body.

Trichinæ are found in the flesh of almost all the mammals. If we eat

this trichinous flesh, the worms become free in the stomach as

digestion goes on, and they are developed with extreme rapidity. Each

female lays a prodigious number of eggs; from each of these comes a

microscopic worm, which bores through the walls of the stomach or the

intestines, and thousands of trichinæ lodge themselves in the flesh,

where they hide till they are again introduced into another stomach.

When the number is great, their presence may cause disorders or even

death. Leuckart's experiments on animals aroused the attention of

physicians, and then it was found that patients who had shewn

exceptional symptoms, had fallen victims to the invasion of these

parasites. Leuckart counted 700,000 trichinæ in a pound of the flesh

of a man, and Zeuker speaks of even five millions found in a similar 246

quantity of human flesh.

The _Trichina spiralis_ produces about a hundred young worms at the

end of a week (viviparous); and a pig which had swallowed a pound of

flesh (5,000,000 trichinæ) might contain after some days 250 millions,

reckoning that only half the worms hatched were females, which is not

the case, for there are more females than males. It appears that

trichinæ can become sexual in all warm-blooded animals, but the number

in which they can become encysted is not so great. It appears that

they are not encysted in birds.

In the month of December, 1863, R. Leuckart wrote to me from Giessen;

"The Trichinæ are playing a great part at present in Germany (with the

exception of Schleswig-Holstein). Two epidemics have made their

appearance within a few months, and have produced a veritable panic,

so that no person will any longer eat pork. The authorities everywhere

are obliged to subject the flesh of these animals to microscopic

examination."

We owe to Leuckart (1856 and 1857) and to Virchow (1858) the knowledge

of the principal facts of the history of these worms. Virchow

ascertained by experiment that they become sexual in the alimentary

canals at the end of three days; and these two naturalists discovered,

after many researches, that trichinæ are neither strongyli nor

trichocephali, but a different kind of nematode, which are hatched in

the stomach of those whom they infest, and that their embryos, instead

of migrating, establish themselves in the host himself. The embryos of

parasites do not usually remain in the animal which gives them

lodging; they are evacuated, as well as the eggs, and are conveyed 247

to another animal. The trichinæ are sexually developed in the same

animal in which they have been engendered.

Worms which produce eggs do not usually hatch them in the same animal;

they are evacuated with the feces. The trichinæ are an exception.

These agamous worms, when introduced into the stomach, rapidly pass

through their evolutions there, become sexual, lay eggs, and the germs

which are produced from them pierce the tissues, and become encysted

in the muscles or other closed organs. It appears that the _Ollulanus

tricuspis_, a nematode of the cat, presents the same phenomena. It is

a species of trichina, which lives at first in the muscles of the

mouse which serves it as a vehicle, then in the stomach of the cat,

where it becomes sexual and complete.

The _Spiroptera obtusa_ is a worm remarkable for its peregrinations.

It passes with the excrements of the mouse into the larva of _Tenebrio

molitor_, which is very fond of it. At the end of a month it is

encysted in this insect, and after five or six weeks it becomes sexual

in the mouse. The _Spiroptera obtusa_ of the mouse lays eggs which are

evacuated with the feces; and these become, with the eggs which they

enclose, the prey of meal worms, the larvæ of the _Tenebrio molitor_,

a coleopterous insect. These germs come forth in the intestine of the

larva, they perforate the intestine and become encysted in the folds

of fat which surround it. Some fine day the insect is swallowed by the

mouse, and the Spiroptera, set at liberty in the intestine, will be

gradually matured until its sexual development is complete.

The ordinary crab of our coasts, _Carcinus mænas_, is the vehicle 248

of a nematode which becomes a _Coronilla robusta_ in the stomach

of a ray.

The _Heteroura androphora_ is another nematode which lives in the

stomach of tritons. The male is always rolled round the body of its

female. The two sexes are always free, contrary to that which is

observed in the syngami. The Blattæ, coleopterous insects, also

harbour sexual nematodes. Radkewisch saw two species of anguillulæ,

the _Anguillula macroura_ and _appendiculata_, in the _Blatta

orientalis_, and an _Oxyuris brachyura_ in the _Blatta germanica_.

These eggs leave the body with the feces, and resist the action of

deleterious agents.

_Heterodera Schachtii_ is the name given to a nematode which Mons.

Schacht discovered on beet-root. This is also a dimorphous worm; the

male has the usual form, the female resembles a lemon. The _Leptodera

appendiculata_ inhabits the foot of the _Arion empiricorum_, in the

larva state, and becomes sexual (male and female) in the decomposed

body of the snail. The next generation has the sexes united, and lives

in damp earth. The _Leptodera pellio_ lives in the same way in the

bodies of lumbrici; another Leptodera inhabits the intestine of the

snail, and a third the salivary glands. The nematode so generally

known under the name of _Ascaris nigro-venosa_ also belongs to this

genus. It lives in the lungs of the frog. There is one also in the

lungs of the toad, but it differs from the preceding.

Leuckart looks upon these worms as females, and their reproduction as

parthenogenetic. Schneider considers that the male exists by the side

of the female sex, and that they are consequently hermaphrodites.

These worms in the lungs are viviparous, and embryos are found in 249

the midst of the intestine of the same animal which gives lodging to

the female. These same worms, proceeding from an hermaphrodite parent,

or from parthogenetic females, live at liberty, and not parasitically

in damp earth or in a decomposed body, and differ from their parents

in size as well as in sexual organs. They all become either male or

female, and consequently their fecundity is dependent upon copulation.

Their parents could all multiply without it, but they cannot. The

females alone produce a new generation.

A worm known by the name of _Vibrio anguillula_ lives in grains of

corn while still green, and multiplies there to a prodigious extent;

it is this which causes the disease known by the name of smut. The

grains grow hard, and enclose nothing but little dried worms, which

remain thus without apparent life, yet without dying, until they are

moistened, when they become damp, the tissues swell, the organs resume

their natural appearance, and the functions are restored at the end of

a few hours.

In a grain of corn affected by smut, anguillulæ without distinct

organs are found, which may be dried and revived eighteen times in

succession, according to Mons. Duvaine, who thinks that these

anguillulæ, leaving an infected grain, come out of their envelopes in

a field of corn, cling to the young stalks, and rise with them. They

begin to develop themselves in the rudimentary flower of the corn, and

acquire genital organs like nematodes. Males and females are always

found separately in a grain of corn.

The ermine lodges in its lungs and tracheal artery a long worm, to 250

which I have given the name of _Filaroides mustelarum_. It usually

forms a little sac, which resembles a tubercle. Many individuals of

different sexes, wound round each other, are so closely tied together

that they can with difficulty be separated. They resemble a ball of

cotton. This filaroid sometimes gets into the frontal sinus, and

mechanically destroys a part of its osseous walls, so that the skull

is pierced by a hole above the frontal sinus. Dr. Weyenberg made this

observation.

It is probable that other species of Mustela will present the same

phenomena, for the skulls of this animal are often to be found

perforated above the orbital cavity.

The _Ollulanus tricuspis_ is a worm which lives in the walls of the

stomach of cats; it is viviparous, and the young ones sometimes wander

into the muscles of their host. But the natural course of things is

that the young are evacuated with the feces, and that these dejecta,

according to all probability, form part of the food of mice, and pass

with them into the cat. It is to be hoped that Leuckart will soon put

this migration out of doubt by a decisive experiment, and will prove

that the mouse serves as a vehicle for three different worms, the

_Cysticercus_, the _Spiroptera obtusa_, and the _Ollulanus tricuspis_.

Many nematodes lodge in the substance of the walls of the gizzard of

birds. In the large goosander we have found one which has round its

head four blades, crossing each other, toothed on the concave side. We

have given the name of _Ascaracantha tenuis_ to this worm. It has

very small eggs. The _Trichosomum crassicauda_ is a nematode of the 251

rat; the female is 2·5 millimètres in length, and the male ·17

millimètres, and it lives in the uterus of its female. Five males are

occasionally found in one female. This observation made by Leuckart

has been confirmed by Bütschli. The male has its digestive tube

incomplete; its female feeds for it.

The bat of the high mountains of Bavaria, known under the name of

_Vespertilio mystacinus_, harbours a nematode, the _Rictularia

plagiostoma_, the same which is found in Egypt in the hedgehog

(_Erinaceus auritus_). The bat on the banks of the Rhine has not this

remarkable worm. We must therefore conclude that the bat of Bavaria

finds and eats the same insect as the hedgehog in Egypt, and that this

insect does not live on the banks of the Rhine. We have never met with

this nematode in the mystacines of Belgium, and yet we have opened

them by hundreds.

A bird found in Florida, the Anhinga, has in its brain a nematode

whose presence in that organ is not accidental.

The _Echinorhynchi_ form a very remarkable group of parasites. They

migrate from one host to another; but the vehicle by which the greater

part of them is conveyed is not known. We represent in Fig. 72 a

species which is very common in the intestine of the sprat.

It is known that these worms migrate when young, and undergo

metamorphoses when they change their host. The _Asellus aquaticus_ of

fresh water, harbours besides other worms, the _Echinorhynchus

hoeruca_; the _Gammarus pulex_, another fresh-water crustacean, lodges

the larva of the _Echinorhynchus proteus_ (Fig. 72). We commonly find

this beautiful species of the Echinorhynchus in the alimentary cavity 252

of the sprat, and it is easily distinguished by its peculiar form and

its orange colour.

[Illustration: Fig. 72.--_Echinorhynchus proteus_ of the Sprat.]

[Illustration: Fig. 73.--Sac with psorospermiæ, in the _Sepia

officinalis_.]

The _Asellus aquaticus_ seems also to serve as the vehicle of the

_Echinorhynchus angustatus_. The hooks of the embryos differ from

those of the adults, as the six hooks of the cestodes differ from the

crown of the adults. Leuckart has described those of the envelope of

the _Echinorhynchus proteus_ and the _Echinorhynchus angustatus_. The

embryo of the Echinorhynchus has only two large hooks on each side,

but several smaller ones. The two species mentioned above have on each

side five or six hooks placed at right angles with the median line,

but they are not all of the same size.

The animals are allied to the _Gordii_ in their development. In fact,

their development is like that of the echinodermata; the larva is the

_Pluteus_, in which the true echinorhynchus develops itself, borrowing

the skin of the pluteus. According to the experiments made by

Schneider, the larvæ of cockchafers must be the vehicles of the 253

_Echinorhynchus gigas_. Pigs disseminate the eggs, and the embryos

infest these larvæ, in the bodies of which they pass through their

principal changes.

The _Gregarinæ_ are microscopic beings, with an extremely simple

organization, the nature and the genealogy of which have only lately

been known. They live at first encysted by thousands together, under

the name of _Psorospermiæ_; they are afterwards hatched in the form of

_Amoebæ_, and then transformed into Gregarinæ. They migrate from one

animal to another, or from one organ to another, to settle in the

intestine, where they assume their adult form. In this state they are

monocellular, and do not at any time possess organs which resemble the

sexual organs of other classes. The disease of silk worms, known by

the name of "pebrine," has been attributed to the development of

psorospermiæ.

We give the representation (Fig. 74) of gregarinæ which we have found

abundantly on the Nemertes; and (Fig. 75) a peculiar species which

lives in the larva of an agrion.

[Illustration: Fig. 74.--Gregarinæ of _Nemertes Gesseriensis_.]

[Illustration: Fig. 75.--_Stylorhynchus oligacanthus_, from the larva

of the Agrion.]

We also give a sketch (Fig. 76) of some very remarkable parasites, 254

whose affinities are still problematical, and which only inhabit

spongy bodies, such as the kidneys of cephalopods. The name of

_Dicyema_ has been given to them.

[Illustration: Fig. 76.--_Dicyema Krohnii_, from Sepia officinalis.]

Prof. Ray Lankester has quite recently made some very interesting

observations, at Naples, on these problematical beings; and my son has

just devoted a part of his vacation, with two of his pupils, to

elucidate the points of their organization and development, which are

still obscure. He went to reside at Villefranche, near Nice, in order

to obtain fresh cephalopods every day. His observations have led him

to a result quite different from that which I expected.