CERTAIN PARASITIC INSECTS.
The subject of our discourse is not only a disagreeable but too often a
painful one. Not only is the mere mention of the creature's name of
which we are to speak tabooed and avoided by the refined and polite, but
the creature itself has become extinct and banished from the society of
the good and respectable. Indeed under such happy auspices do a large
proportion of the civilized world now live that their knowledge of the
habits and form of a louse may be represented by a blank. Not so with
some of their great-great-grandfathers and grandmothers, if history,
sacred and profane, poetry,[5] and the annals of literature testify
aright; for it is comparatively a recent fact in history that the louse
has awakened to find himself an outcast and an alien. Among savage
nations of all climes, some of which have been dignified with the apt,
though high sounding name of Phthiriophagi, and among the Chinese and
other semi-civilized peoples, these lords of the soil still flourish
with a luxuriance and rankness of growth that never diminishes, so that
we may say without exaggeration that certain mental traits and fleshly
appetites induced by their consumption as an article of food may have
been created, while a separate niche in our anthropological museums is
reserved for the instruments of warfare, both offensive and defensive,
used by their phthiriophagous hunters. Then have we not in the very
centres of civilization the poor and degraded, which are most faithfully
attended lay these revolting satellites!
But bantering aside, there is no more engaging subject to the naturalist
than that of animal parasites. Consider the great proportion of animals
that gain their livelihood by stealing that of others. While a large
proportion of plants are more or less parasitic, they gain, thereby in
interest to the botanist, and many of them are eagerly sought as the
choicest ornaments of our conservatories. Not so with their zoölogical
confréres. All that is repulsive and uncanny is associated with them,
and those who study them, though perhaps among the keenest intellects
and most industrious observers, speak of them without the limits of
their own circle in subdued whispers or under a protest, and their works
fall under the eyes of the scantiest few. But the study of animal
parasites has opened up new fields of research, all bearing most
intimately on those two questions that ever incite the naturalist to the
most laborious and untiring diligence--what is life and its origin? The
subjects of the alternation of generations, or parthenogenesis, of
embryology and biology, owe their great advance, in large degree, to the
study of such animals as are parasitic, and the question whether the
origin of species be due to creation by the action of secondary laws or
not, will be largely met and answered by the study of the varied
metamorphoses and modes of growth, the peculiar modification of organs
that adapt them to their strange modes of life, and the consequent
variation in specific characters so remarkably characteristic of those
animals living parasitically upon others.[6]
With these considerations in view surely a serious, thoughtful, and
thorough study of the louse, in all its varieties and species, is
neither belittling nor degrading, nor a waste of time. We venture to
say, moreover, that more light will be thrown on the classification and
morphology of insects by the study of the parasitic species, and other
degraded, wingless forms that do not always live parasitically,
especially of their embryology and changes after leaving the egg, than
by years of study of the more highly developed insects alone. Among
Hymenoptera the study of the minute Ichueumons, such as the
Proctotrupids and Chalcids, especially the egg-parasites; among moths
the study of the wingless canker-worm moth and Orgyla; among Diptera the
flea, bee louse, sheep tick, bat tick, and other wingless flies; among
Coleoptera, the Meloë, and singular Stylops and Xenos; among Neuroptera,
the snow insect, Boreus, the Podura (Fig. 109) and Lepisma, and
especially the hemipterous lice, will throw a flood of light on these
prime subjects in philosophical entomology.
[Illustration: 109. Podura.]
Without farther apology, then, and very dependent on the labors of
others for our information, we will say a few words on some interesting
points in the natural history of lice. In the first place, how does the
louse bite? It is the general opinion among physicians, supported by
able entomologists, that the louse has jaws, and bites. But while the
bird lice (Mallophaga) do have biting jaws, whence the Germans call them
skin-eaters (_pelzfresser_), the mouth parts of the genus Pediculus, or
true louse, resemble in their structure those of the bed-bug (Fig. 110),
and other Hemiptera. In its form the louse closely resembles the
bed-bug, and the two groups of lice, the Pediculi and Mallophaga, should
be considered as families of Hemiptera, though degraded and at the base
of the hemipterous series. The resemblance is carried out in the form of
the egg, the mode of growth of the embryo, and the metamorphosis of the
insect after leaving its egg.
[Illustration: 110. Bed-bug.]
Schiödte, a Danish entomologist, has, it seems to us, forever settled
the question as to whether the louse bites the flesh or sucks blood, and
decides a point interesting to physicians, _i.e._, that the loathsome
disease called phthiriasis is a nonentity. From this source not only
many living in poverty and squalor are said to have died, but also men
of renown, among whom Denny in his work on the Anoplura, or lice, of
Great Britain, mentions the name of "Pheretima, as recorded by
Herodotus, Antiochus Epiphanes, the Dictator Sylla, the two Herods, the
Emperor Maximian, and Phillip the Second." Schiödte, in his essay "On
Phthirius, and on the Structure of the Mouth in Pediculus" (Annals and
Magazine of Natural History, 1866, page 213), says that these statements
will not bear examination, and that this disease should be placed on the
"retired list," for such a malady is impossible to be produced by simply
blood-sucking animals, and that they are only the disgusting attendants
on other diseases. Our author thus describes the mouth parts of the
louse.
"Lice are no doubt to be regarded as bugs, simplified in structure and
lowered in animal life in accordance with their mode of living as
parasites, being small, flattened, apterous, myopic, crawling and
climbing, with a conical head, moulded as it were to suit the rugosities
of the surface they inhabit, provided with a soft, transversely furrowed
skin, probably endowed with an acute sense of feeling, which can guide
them in that twilight in which their mode of life places them. The
peculiar attenuation of the head in front of the antennæ at once
suggests to the practised eye the existence of a mouth adapted for
suction. This mouth differs from that of the Hemiptera (bed-bug, etc.)
generally, in the circumstance that the labium is capable of being
retracted into the upper part of the head, which therefore presents a
little fold, which is extended when the labium is protruded. In order to
strengthen this part, a flat band of chitine is placed on the under
surface, just as the shoemaker puts a small piece of gutta-percha into
the back of an India-rubber shoe; as, however, the chitine is not very
elastic, this band is rather thinner in the middle, in order that it may
bend and fold a little when the skin is not extended by the lower lip.
The latter consists, as usual, of two hard lateral pieces, of which the
fore ends are united by a membrane so that they form a tube, of which
the interior covering is a continuation of the elastic membrane in the
top of the head; inside its orifice there are a number of small hooks,
which assume different positions according to the degree of protrusion;
if this is at its highest point the orifice is turned inside out, like a
collar, whereby the small hooks are directed backwards, so that they can
serve as barbs. These are the movements which the animal executes after
having first inserted the labium through a sweat-pore. When the hooks
have got a firm hold, the first pair of setæ (the real mandibles
transformed) are protruded; these are, towards their points, united by a
membrane so as to form a closed tube, from which, again, is inserted the
second pair of setæ, or maxillæ, which in the same manner are
transformed into a tube ending in four small lobes placed crosswise. It
follows that when the whole instrument is exserted, we perceive a long
membranous flexible tube hanging down from the labium, and along the
walls of this tube the setiform mandibles and maxillæ in the shape of
long narrow bands of chitine. In this way the tube of suction can be
made longer or shorter as required, and easily adjusted to the thickness
of the skin in the particular place where the animal is sucking, whereby
access to the capillary system is secured at any part of the body. It is
apparent, from the whole structure of the instrument, that it is by no
means calculated on being used as a sting, but is rather to be compared
to a delicate elastic probe, in the use of which the terminal lobes
probably serve as feelers. As soon as the capillary system is reached,
the blood will at once ascend into the narrow tube, after which the
current is continued with increasing rapidity by means of the pulsation
of the pumping ventricle and the powerful peristaltic movement of the
digestive tube."
[Illustration:[7]111. Mouth of the Louse.]
If we compare the form of the louse (Fig. 112, Pediculus capitis, the
head louse; Fig. 113, P. vestimenti, the body louse) with the young
bed-bug as figured by Westwood (Modern Classification of Insects, ii,.p.
475) we shall see a very close resemblance, the head of the young Cimex
being proportionally larger than in the adult, while the thorax is
smaller, and the abdomen is more ovate, less rounded; moreover the body
is white and partially transparent.
[Illustration: 113. Body Louse.]
[Illustration: 112. Head Louse.]
Under a high power of the microscope specimens treated with diluted
potash show that the mandibles and maxillæ arise near each other in the
middle of the head opposite the eyes, their bases slightly diverging.
Thence they converge to the mouth, over which they meet, and beyond are
free, being hollow, thin bands of chitine, meeting like the maxillæ, or
tongue, of butterflies to form a hollow tube for suction. The mandibles
each suddenly end in a curved, slender filament, which is probably used
as a tactile organ to explore the best sites in the flesh of their
victim for drawing blood. On the other hand the maxillæ, which are much
narrower than the mandibles, become rounded towards the end, bristle
like, and tipped with numerous exceedingly fine barbs, by which the bug
anchors itself in the flesh, while the blood is pumped through the
mandibles. The base of the large, tubular labium, or beak, which
ensheathes the mandibles and maxillæ, is opposite the end of the clypeus
or front edge of the upper side of the head, and at a distance beyond
the mouth equal to the breadth of the labium itself. The labium, which
is divided into three joints, becomes flattened towards the tip, which
is square, and ends in two thin membranous lobes, probably endowed with
a slight sense of touch. On comparing these parts with those of the
louse, it will be seen how much alike they are with the exception of the
labium, a very variable organ in the Hemiptera. From the long sucker of
the Pediculus, to the stout chitinous jaws of the Mallophaga, or bird
lice, is a sudden transition, but on comparing the rest of the head and
body it will be seen that the distinction only amounts to a family one,
though Burmeister placed the Mallophaga among the Orthoptera
(grasshoppers and crickets) on account of the mandibles being adapted
for biting. It has been a common source of error to depend too much upon
one or a single set of organs. Insects have been classified on
characters drawn from the wings, or the number of the joints of the
tarsi, or the form of the mouth parts. We must take into account in
endeavoring to ascertain the limits of natural groups, as the internal
anatomy and the embryology and metamorphosis of insects, before we can
hope to obtain a natural classification.
The family of bird lice is a very extensive one, embracing many genera,
and several hundred species. One or more species infest the skin of all
our domestic and wild mammals and birds, some birds sheltering beneath
their feathers four or five species of lice. Before giving a hasty
account of some of our more common species; we will give a sketch of the
embryological history of the lice, with special reference to the
structure of the mouth parts.
[Illustration: 114. Embryo of the Louse.]
[Illustration: 115. Mouth Parts of the Louse.]
The eggs (Fig. 114, egg of the head louse) are long, oval, somewhat
pear-shaped, with the hinder end somewhat pointed, while the anterior
end is flattened, and bears little conical micropyles (_m_, minute
orifices for the passage of the spermatozoa into the egg), which vary in
form in the different species and genera; the opposite end of the egg is
provided with a few bristles. The female attaches her eggs to the hairs
or feathers of her host.
[Illustration: 116. Mouth Parts of the Louse.]
[Illustration: 118. Mouth Parts of Louse.]
[Illustration: 117. Mouth Parts of Louse.]
After the egg has been fertilized by the male, the blastoderm, or
primitive skin, forms, and subsequently two layers, or embryonal
membranes, appear; the outer is called the amnion (Fig. 114, _am_),
while the inner visceral membrane (_db_) partially wraps the rude form
of the embryo in its folds. The head (_vk_) of the embryo is now
directed towards the end of the egg on which the hairs are situated;
afterwards the embryo revolves on its axis and the head lies next to the
opposite end of the egg. Eight tubercles bud out from the under side of
the head, of which the foremost and longest are the antennæ (_as_),
those succeeding are the mandibles, maxillæ, and second maxillæ, or
labium. Behind them arise six long, slender tubercles forming the legs,
and the primitive streak rudely marks the lower wall of the thorax and
abdomen not yet formed. Figure 115 represents the head and mouth parts
of the embryo of the same louse; _vk_ is the forehead, or clypeus;
_ant_, the antennæ; _mad_, the mandibles; _max_1, the
first pair of maxillæ, and _max_^2, the second pair
of maxillæ, or labium. Figure 116 represents the mouth parts of the
same insect a little farther advanced, with the jaws and labium
elongated and closely folded together. Figure 117 represents the same
still farther advanced; the mandibles (_mad_) are sharp, and resemble
the jaws of the Mallophaga; and the maxillæ (_max_^1) and labium
(_max_^2) are still large, while afterwards the labium becomes nearly
obsolete. Figure 118 represents a front view of the mouth parts of a
bird louse, Goniodes; _lb_, is the upper lip, or labrum, lying under the
clypeus; _mad_, the mandibles; max, the maxillæ; _l_, the lyre-formed
piece; and _pl_, the "plate."
[Illustration: 119. Louse of Cow.]
We will now describe some of the common species of lice found on a few
of our domestic animals, and the mallophagous parasites occurring on
certain mammals and birds. The family Pediculina, or true lice, is
higher than the bird lice, their mouth parts, as well as the structure
of the head, resembling the true Hemiptera, especially the bed bug. The
clypeus, or front of the head, is much smaller than in the bird lice,
the latter retaining the enlarged forehead of the embryo, it being in
some species half as large as the rest of the head.
All of our domestic mammals and birds are plagued by one or more species
of lice. Figure 119 represents the Hæmatopinus vituli, which is brownish
in color. As the specimen figured came from the Burnett collection of
the Boston Society of Natural History, together with those of the goat
louse, the louse of the common fowl, and of the cat, they are
undoubtedly naturalized here. Quite a different species is the louse of
the hog (H. suis, Fig. 120).
[Illustration: 120. Louse of Hog.]
The remaining parasites belong to the skin-biting lice, or Mallophaga,
and I will speak of the several genera referred to in their natural
order, beginning with the highest form and that which is nearest allied
to Pediculus.
[Illustration: 121. Louse of Domestic Fowl.]
The common barn-yard fowl is infested by a louse that we have called
Goniocotes Burnettii (Fig. 121), in honor of the late Dr. W. I. Burnett,
a young and talented naturalist and physiologist, who paid more
attention than any one else in this country to the study of these
parasites, and made a large collection of them, now in the museum of the
Boston Society of Natural History. It differs from the G. hologaster of
Europe, which lives on the same bird, in the short second joint of the
antennæ, which are also stouter; and in the long head, the clypeus being
much longer and more acutely rounded; while the head is less hollowed
out at the insertion of the antennæ. The abdomen is oval, and one-half
as wide as long, with transverse, broad, irregular bands along the edges
of the segments. The mandibles are short and straight, two toothed. The
body is slightly yellowish, and variously streaked and banded with
pitchy black. The duck is infested by a remarkably slender form (Fig.
122, Philopterus squalidus). Figure 123 represents the louse of the cat,
and another species (Fig. 124) of the same genus (Trichodes) lives upon
the goat.
The most degraded genus is Gyropus. Mr. C. Cook has found Gyropus ovalis
of Europe abundant on the Guinea pig. A species is also found on the
porpoise; an interesting fact, as this is the only insect we know of
that lives parasitically on any marine animal.
[Illustration: 122. Duck Louse.]
The genus Goniodes (Fig. 125, G. stylifer, the turkey louse) is of great
interest from a morphological and developmental point of view, as the
antennæ are described and figured by Denny as being "in the males
cheliform (Fig. 126, _a_, male; _b_, female); the first joint being very
large and thick, the third considerably smaller, recurved towards the
first, and forming a claw, the fourth and fifth very small, arising
from the back of the third." He farther remarks, that "the males of this
[which lives on the turkey] and all the other species of Goniodes, use
the first and third joints of the antennæ with great facility, acting
the part of a finger and thumb." The antennæ of the females are of the
ordinary form. This hand-like structure, is, so far as we know, without
a parallel among insects, the antennæ of the Hemiptera being almost
uniformly filiform, and from two to nine-jointed. The design of this
structure is probably to enable the male to grasp its consort and also
perhaps to cling to the feathers, and thus give it a superiority over
the weaker sex in its advances towards courtship. Why is this advantage
possessed by the males of this genus alone? The world of insects, and of
animals generally abounds in such instances, though existing in other
organs, and the developmentist dimly perceives in such departures from a
normal type of structure, the origin of new generic forms, whether due
at first to a seemingly accidental variation, or, as in this instance,
perhaps, to long use as prehensile organs through successive generations
of lice having the antennæ slightly diverging from the typical
condition, until the present form has been developed. Another generation
of naturalists will perhaps unanimously agree that the Creator has thus
worked through secondary laws, which many of the naturalists of the
present day are endeavoring, in a truly scientific and honest spirit of
inquiry, to discover.
[Illustration: 124. Louse of the Goat.]
[Illustration: 123. Louse of the Cat.]
In their claw or leg-like form these male antennæ also repeat in the
head, the general form of the legs, whose prehensile and grasping
functions they assume. We have seen above that the appendages of the
head and thorax are alike in the embryo, and the present case is an
interesting example of the unity of type of the jointed appendages of
insects, and articulates generally.
[Illustration: 120. Antennæ of Goniodes.]
Another point of interest in these degraded insects is, that the process
of degradation begins either late in the life of the embryo or during
the changes from the larval to the adult, or winged state. An instance
of the latter may be observed in the wingless female of the canker worm,
so different from the winged male; this difference is created after the
larval stage, for the caterpillars of both sexes are the same, so far as
we know. So with numerous other examples among the moths. In the louse,
the embryo, late in its life, resembles the embryos of other insects,
even Corixa, a member of a not remotely allied family. But just before
hatching the insect assumes its degraded louse physiognomy. The
developmentist would say that this process of degradation points to
causes acting upon the insect just before or immediately after birth,
inducing the retrogression and retardation of development, and would
consider it as an argument for the evolution of specific forms by causes
acting on the animal while battling with its fellows in the struggle for
existence, and perhaps consider that the metamorphoses of the animal
within the egg are due to a reflex action of the modes of life of the
ancestors of the animal on the embryos of its descendants.
[Illustration: 125. The Turkey Louse.]
FOOTNOTES:
[Footnote 5:
Ha! whare ye gaun, ye crowlin ferlie!
Your impudence protects you sairly:
I canna say but ye struift rarely,
Owre gauze and lace;
Tho' faith, I fear ye dine but sparely
On sic a place.
Ye ugly, creepin, blastic wormer,
Detested, shunn'd by saunt and sinner,
How dare ye set your fit upon her
Sae fine a lady!
Gae somewhere else and seek your dinner
On some poor body.
(To a Louse.--Burns.)]
[Footnote 6: We notice while preparing this article that a journal of
Parasitology has for some time been issued in Germany--that favored land
of specialists. It is the "Zeitschrift fur Parasitenkunde," edited by
Dr. E. Hallier and F A. Zurn. 8vo, Jena.]
[Footnote 7: Figure 111 represents the parts of the mouth in a large
specimen of _Pediculus_ vestimenti, entirely protruding, and seen from
above, magnified one hundred and sixty times; aa, the summit of the head
with four bristles on each side; _bb_, the chitinous band, and _c_, the
hind part of the lower lip, such as they appear through the skin by
strong transmitted light; _dd_, the foremost protruding part of the
lower lip (the haustellum); _ee_, the hooks turned outwards; _f_, the
inner tube of suction, slightly bent and twisted; the two pairs of jaws
are perceived on the outside as thin lines; a few blood globules are
seen in the interior of the tube.]