AQUATIC INSECT LARVAE
In this chapter we shall deal with a few aquatic insect larvae. Of
these, some are aquatic also in the perfect condition, while others
emerge from the pupa stage as aërial insects. It requires no great
amount of care to keep these creatures, and some hints on this subject
and on collecting are given in the first chapter.
The larva of Dytiscus is abundant during the greater part of the year,
and is almost sure to be met with by the collector, who will find it
an extremely interesting object for examination and study. No other
creatures should be put in the same bottle with these larvae; and if
there are several of them in one bottle, it is a good plan to put in
plenty of pondweed, which will often keep them from attacking each
other.
When full grown, the Dytiscus larva may attain a length of two inches
or rather more. Its colour is dingy brown, and its aspect forbidding
enough to justify the uncomplimentary names that have been bestowed
upon it--Water-devil and Water-tiger. It certainly rivals the tiger in
fierceness, and its method of stealing up to its prey and attacking it
from behind led Swammerdam to call it the Sicarius or Assassin Worm.
One must not imagine that Swammerdam was ignorant of its nature; ‘worm’
with him was a general term for any larval form. Indeed, he says,
‘It is extremely probable that some peculiar species of the Water
Beetle proceeds from this worm, when, having remained in the water a
sufficient time, it betakes itself to the land to undergo its mutation;
but this is mere conjecture.’ What was conjecture for him is fact for
us.
Now let us put our larva into a small tube, and examine it more
closely. The head is large and joined to the first segment of the
thorax by a distinct neck. There are twelve small eyes, six on each
side, a pair of antennae, two pairs of palps, and a large pair of
sickle-shaped mandibles, which Swammerdam calls ‘teeth,’ and says that
‘it is perhaps to contain the muscles such teeth require that Nature
has made the head so large.’ Behind the head come eleven segments, of
which the first and last are the longest. They gradually increase in
width till the sixth, the rest again decreasing, till the eleventh ends
in a blunt point, from which diverge two appendages, thus [image],
thickly fringed on both sides with hair, as are the tenth and eleventh
segments.
There are six legs, one pair to each of the first three segments.
These also carry fringes of hair, thus increasing their power as
swimming organs; and, in addition, they bear numerous spines, and end
in strong double claws, which must be of service in climbing over
aquatic vegetation, and may assist in holding a struggling victim or in
striking it down, so as to bring it within reach of the mandibles.
Spiracles will be found--seven on each side. These do not, however, in
the larval condition, serve as breathing organs, though they fulfil
their proper office in the pupa. The air-tubes of the larva open at the
extremity of the last segment. When the larva wants to breathe it comes
to the surface without an effort, for it is lighter than the water it
displaces. The tail rises above the surface, and a fresh supply of air
is taken in. When the larva wishes to descend, a stroke of the tail
sends it downwards, and as it reaches the bottom of the tube it will
cling with its claws to any weed we may have put in with it, or hold on
with them to the glass itself.
The chief interest of this animal lies in its mandibles, and the method
in which they are employed. It was formerly believed that the mouth of
this larva was closed, so that it could not take solid food, and that
it lived entirely on the juices of its prey, which it sucked up through
its hollow mandibles.
Swammerdam says of this larva, ‘When about to eat he seizes with the
two teeth (mandibles) the little creatures that come in his way, and
pierces their body with the sharp crooked points. The teeth being
perforated from the points to the roots, he in a surprising manner
sucks through them into his mouth the blood of the unfortunate captive.
This may be easily seen, especially when the blood of his prey is of a
red colour, as the teeth are transparent.’
He then describes how he watched one of these larvae feed, and saw the
blood, mixed with air-bubbles, travel up the mandibles. After this he
tells us how, if we have a Dytiscus larva, we may ‘procure ourselves
a very entertaining and surprising sight, by throwing to it a small
earthworm; for let this last move, twine, and otherwise bestir itself
ever so much, the other keeps its hold, and very calmly sucks the blood
of its prisoner.’
We may, however, go to work in another fashion. We may dissect out the
mandibles from a dead larva and pass a fine hair into the slit near the
point, and it will come out at the orifice near the base. It is through
this orifice that the nutritive juices of the prey are drawn into the
true mouth. This practical proof that the mandibles are pierced is by
no means so difficult as one might suppose.
De Geer[57] seems to have been the first to suggest that there must
be some kind of true mouth, and in support of his suggestion tells us
that he saw this larva eating up the solid parts of a Water Woodlouse
(_cloporte_), after having sucked up its juices. More than this,
he places the mouth in what has proved to be the true position, though
he did not solve the mystery as to why it is kept so firmly closed.
This was done by Mr. Burgess, an American naturalist, from whose
paper[58] the following particulars are condensed:--
‘Authors have described this creature as mouthless; and if we examine
the slit where we should expect the mouth to be, we find that this slit
ends in a perfectly closed seam. The methods of microscopical research
were brought into play, and a longitudinal section of the head cut and
mounted. This showed that the upper and lower lips were locked together
by a peculiar joint--the upper coming over and locking into the under
lip (Fig. 75).’
We may get some idea of this mouth-lock by placing the fingers of the
right hand over those of the left, and then bending them.
Mr. Burgess concludes his paper thus: ‘We find that the Water-tiger,
far from being mouthless, as ordinarily assumed, has in fact a
very wide mouth, though its lips are closely locked together by a
dove-tailed grooved joint developed for this purpose. Whether this
joint can be unlocked by the animal itself is another question, which
I cannot answer, though De Geer’s observation above quoted makes this
probable. It is, at all events, easy to open the mouth by manipulation
with a pair of forceps.’
[Illustration: FIG. 75.--Mouth-lock. _m_, mouth ×
125. (After Burgess.)]
Professor Miall[59] has verified Burgess’s observations, and carried
them a step further. He found by actual experiment that ‘the mouth-lock
acted automatically, opening when the mandibles opened, and closing
when they closed.’
Both these authorities stand very high. Yet, with all respect to them,
it will be well to test these statements before accepting them.
Something of this mouth-lock may be seen in any well-prepared slide
of a Dytiscus larva. If we hold the slide up to the light and examine
with a power of 10, we shall see a dark line--in some cases two nearly
parallel thinner lines--running from the base of one mandible to the
base of the other. The dark line is the closed mouth-lock. The two
nearly parallel thinner lines are the edges of the lips drawn asunder
in preparing the specimen or by the pressure of the cover-glass. If we
get to see this much, we shall have advanced one step.
[Illustration: FIG. 76.--Dytiscus Larvae.]
Next we may verify Professor Miall’s experiment, though not quite in
his way, for such section-cutting as he speaks of is beyond our powers.
Larvae as large as possible should be chosen, and killed by dropping
them into boiling water. The mandibles of one should be allowed to
remain closed, and those of the other plugged open with pith or a small
piece of wood--a bit of a match will serve. By putting each in turn
into an excavated slip with water, carefully covering this with a plain
slip, and holding these slips together with an elastic band, we may
examine the larvae as we did the slide.
The result will be practically the same. Where the mandibles are
closed, we shall see the dark line; and where they are open, we shall
see the two thinner ones nearly parallel.
One caution may be necessary. The mandibles bear at the base a
rounded process, which fits into a chitinous cup. It is not difficult
to mistake this for the mouth-lock, with which, however, it is not
connected.
There is still one other method which we may adopt to see the mouth.
The head of one of these larvae may be cut off, dropped into a strong
solution of caustic potash, where it should remain for a day or two.
After washing it well in water, cut it in half lengthways, and turning
either half upon its side, so as to expose the part cut, examine with
the pocket lens.
These experiments are by no means difficult. But if carried out step
by step, it will be easy to understand how the larva can suck out the
juices of its prey, and how it can open its mouth to swallow some of
the solid parts.
The larva does not readily change into a pupa in confinement. If,
however, we wish to rear a beetle, the larva must be plentifully
supplied with food, and removed from a bottle to a flat dish,
where earth can be placed against the side so as to rise above the
water-level. Fig. 77, where a pupa is represented in a bank by the side
of a pond, will give us a hint how to go to work. The time occupied in
pupation will vary according to the temperature of the room--but is
never less than a fortnight. In the open it is probable that the winter
is passed in the pupal condition, the perfect insect emerging in the
spring. Like Land Beetles, it does not assume its dark hue for some
days, but its pale skin darkens by degrees.
[Illustration: FIG. 77.--Pupa of Dytiscus.]
The larva of Hydrophilus does not seem to be often taken in this
country. It would make a capital subject for investigation, and the
food-supply could be arranged easily enough. The repetition of the
experiences of Lyonnet, who reared these larvae from the egg, would
be of great interest. He says that he took about thirty larvae from
the brood, and fed them with very small water-snails. These they
devoured in the same way as the larger larvae do. Having seized the
snail with their mandibles, they bent backwards, and supporting it
on their back, which served them for a table, eat it there, without
making any use of their legs to hold their prey. When the supply of
small snails ran short, they did very well with large ones cut up into
pieces, and with tadpoles. If, however, food was not supplied to them,
they fed on each other. But, except when pressed by hunger, they lived
together peaceably enough, and seemed to take pleasure in each other’s
society[60].
The larva of _Limnobia replicata_, a Crane-fly allied to, but
smaller than, the well-known Daddy-longlegs, is another excellent
subject for investigation. It is not very often taken; perhaps because
it is not often looked for. But it is common enough, for all that.
In general appearance these larvae resemble small caterpillars covered
with spines. Some of these are simple and others forked, not much
unlike the letter [image], with a short stem, and the arms slightly
curved. There are no feet, and the last segment carries two pairs of
hooks, one large and the other small. From their position they are
called anal hooks.
The dykes of the Sussex marshes are an excellent hunting-ground.
Probably the channels of water-meadows, or any other shallow standing
water in which aquatic moss grows, would serve the collector’s purpose
quite as well. And such pieces of water abound all over the country.
For taking these larvae the ordinary net and bottle are of little use,
though a few may be captured by sweeping backwards and forwards among
patches of aquatic moss.
There is, however, a far easier and surer method. A good handful of
the moss should be gathered, and put into a shallow vessel half full
of water--a developing-dish answers capitally--and then shaken to and
fro or gently stirred with a small piece of stick. The larvae will curl
into a ring and fall to the bottom, whence they may be picked up and
dropped into a bottle or other receptacle to be taken home. A fair
quantity of moss should be gathered, for this is their favourite food,
and all larvae are greedy feeders.
Other water-plants, however, do not come amiss to them. Just before
these lines were written I was examining a bottle in which some of
these larvae were kept. It contained a few sprays of willow-moss and
some ivy-leaved duckweed, which floated on the surface. One larva on a
spray of moss was reaching upward, and it was distinctly seen to feed
on the duckweed. This must have been from choice, for there was within
reach plenty of what all observers consider to be its natural food.
This, too, might have been more easily obtained; for, to reach the
duckweed, the larva had to hold on to the moss by the anal hooks, and
extend its body in a fashion analogous to that of the caterpillar of a
geometer moth, which will hold on to a branch with its fore-legs and
claspers and maintain the body at an angle of 45°, sometimes for hours
together. I have also seen them feed on hornwort.
The larva of this small Crane-fly is not at all difficult to keep. It
is exceedingly hardy, and will survive a great deal of rough treatment.
In November, 1895, I sent three in a tube--securely packed, as I
thought--to a friend in Yorkshire. A few days afterwards I heard, with
regret, ‘that the bottle was broken in transit, and that the larvae
arrived dead.’ Three days later I was gratified by receiving a letter,
from which the following is quoted: ‘The Limnobia larvae have come to
life again. I put them into water as soon as they arrived, and after
lying motionless for many hours they have begun to creep about and
feed.’
This is excellent testimony to their powers of endurance, but it is
weak in comparison to that which De Geer supplies[61].
He was Marshal of the Court of Sweden, and one November, before leaving
his country house for his official duties at Stockholm, he put four
of these larvae into a vessel of water, and left them to take their
chance. The water froze into a solid mass. When he returned in the
following May he found about half the water thawed, and two of the
larvae dead. The others, though they had been enclosed in ice all the
winter, were lively and in good condition. He put them into another
vessel with fresh water and some aquatic moss, and at once they began
to move about and commenced to feed. Both pupated by the fifteenth of
the month, and the perfect fly emerged after six days in the pupal
stage.
[Illustration: FIG. 78.--Larva of _Limnobia
replicata_.]
The following description of this larva is principally condensed from
De Geer, whence the figures are also taken. The body is long and
cylindrical, and divided into eleven segments, of which the first and
largest is sub-triangular. The second and third segments are shorter
than the rest.
The head (_t_) is very small and completely retractile within
the first segment, the anterior margin of which completely closes
the orifice, so that, in this condition, the creature appears to be
headless. The body is covered with spines, some simple and others
branched. On the first three segments there are only simple spines;
but from the fourth to the tenth segment inclusive there are also on
each segment two forked spines--that is, fourteen in all. On the last
segment the spines are simple, and here are also four chitinous hooks,
one pair much larger than the other. These simple spines carry a white
vessel, which extends throughout their whole length; but in the forked
spines there are two such vessels placed side by side in the stem, and
diverging one to each branch.
He comes to the conclusion that these spines are probably the breathing
apparatus of the larva, for they are similar to those which he observed
in an aquatic caterpillar. Walker[62] calls these spines ‘long
filamentous processes, which appear to be internally supplied with
air-tubes,’ but he does not seem to have taken the trouble to break up
a specimen, or he would have been in no doubt as to their real nature.
This is shown by the fact that the larva never comes to the surface to
take in a supply of air, but contents itself with the oxygen dissolved
in the water.
[Illustration:
FIG. 79.--Forked spine of Limnobia, enlarged; the dark
lines show air-tubes.]
The pupa is quite as remarkable as the larva, though the breathing
apparatus does not assume the form of spines, but consists of two
‘trumpets,’ one on each side of the head, as is the case with the
pupae of gnats, using that term in a wide sense. The colour is a
greenish-brown, dotted with black. The abdomen is capable of a good
deal of motion from side to side; and by this means the pupa can raise
itself to the surface of the water to take in a supply of air.
De Geer remarked that when the pupa rose for this purpose it lay with
its body horizontal, having the lips of the trumpets a little above the
surface. It appeared not to like being placed on its back, because in
that position the trumpets cannot be raised above the surface. When he
tried the experiment of putting the pupa back downwards, it wriggled
over by bending the abdomen.
[Illustration: FIG. 80.--Pupa case of Limnobia.
(From a photograph taken at the Yorkshire College, Leeds.)]
On the abdomen there are several chitinous hooks, which serve in some
sort as substitutes for limbs. By their means the pupa can moor itself
to the stems of aquatic plants; and this is necessary, since its
specific gravity being less than that of the water it would be always
at the surface, if it had no such means of anchorage. And of course,
at the top of the water, it would be exposed to the danger of being
snapped up by birds.
De Geer’s specimen passed six days in the pupal state, and then emerged
as a perfect Crane-fly. My specimens did not emerge till after ten and
eleven days of pupahood, which seems strange, as they were plentifully
supplied with food in their larval stage.
The fly is a little more than half an inch long, and may be
distinguished from the common Daddy-longlegs by the character of the
wings, which are folded somewhat like those of a wasp, but with this
difference: that the wings of this fly are folded outward, while those
of the wasp are folded inwards. When the insect wishes to fly, it opens
the fold so that the whole wing presents a plane surface, but the fold
reappears directly the Crane-fly ceases its flight (Frontispiece).
[Illustration: FIG. 81.--Fore-wing of Bee, showing
marginal fold (× 7).]
De Geer’s allusion to the wing of the wasp might have been extended
to most of the Hymenoptera, as we may see by examining the fore and
hind wings of a bee or a sawfly. Dr. Sharp[63] says, ‘The wings [of
the Hymenoptera] are remarkable for the beautiful manner in which the
hinder one is united to the anterior one, so that the two act in flight
as a single organ. The hind wing is furnished with a series of hooks,
and the hind margin of the front wing is curled over so that the hooks
catch on to it. In some of the parasitic forms the wings ... have no
hooks. The powers of flight, in these cases, are probably but small.’
If we were taking our subjects in consecutive order, the larva of
Ptychoptera would properly come here, as being that of a Crane-fly. But
since it will be convenient to examine another larva which resemble
Limnobia in its breathing apparatus, we will take next the larva of
_Parap´onyx stratiota´ta_, one of the China Marks, for it is
extremely interesting and by no means hard to come by.
The China Marks are small moths, with white wings bearing dark
markings, which have been supposed to resemble Chinese characters.
Their larvae are aquatic in varying degree--that is, some breathe air
in the usual way, by means of spiracles; while others, by means of
gills, breathe the oxygen dissolved in the water.
Many collectors have, no doubt, taken these larvae, and cast them away
in the belief that they were caddis-worms. Such was the experience of
the Rev. Gregory Bateman, the author of _Fresh-water Aquaria_,
who says (p. 259): ‘While hunting for fresh-water animals, one not
seldom comes across an insect wrapped up in two or more green leaves,
or pieces of leaves, of some aquatic plant. The leaves and the animal
have somewhat the appearance of a caddis-worm in its case; in fact, for
a time, before I knew what it was, I mistook it (and I daresay others
have done so also) for a caddis-worm.’
The cases are usually, but not invariably, made from the food-plant
of the insect. Mr. Bateman has noted that these larvae ‘do not
always confine themselves to the same weed, either for food or for
building material.’ This has also been my experience. A larva of the
Brown China Mark, recently taken on the Norfolk Broads--an excellent
collecting ground for aquatic larvae--was put into a tube. The case
had been damaged, and the only vegetation in the tube was a spray of
bladderwort. On examining the tube, after some days, I failed to find
the larva. The reason was evident on removing the cork, a small part
of which had been gnawed away to procure material for the repair of
the larval case, which was affixed to the under side. The larva was
dead and too much decayed to be put into pickle, a circumstance I much
regret, as I should like to have preserved the larva in such a strange
dwelling. As it is, I have only been able to keep the house without its
tenant.
Pondweed is the usual home of the larva of the Brown China Mark, and
from the leaves of this plant the first larval case is generally
fashioned. This was the species upon which Réaumur made his interesting
observations, most of which have been confirmed by succeeding
observers. In well-grown larvae the contrivance by which the animal
is protected from contact with the water in which it lives should be
noted, as it may be easily, with the hand lens. The skin is thickly set
with tiny protuberances between which the water cannot penetrate, the
surface film stretching from tip to tip of these prominences, just as
it does over the hairs that cover the body of a water-spider.
De Geer[64] describes an aquatic larva of one of the China Marks
(_Paraponyx stratiotata_), which has its breathing apparatus
fashioned on a similar plan to that of Limnobia, though there is some
difference in the details. He found his specimens on the leaves of the
Water Soldier, and his interesting account recalls the fact to memory
that this remarkable plant was at one time called the Marsh Aloe--an
exceedingly appropriate name.
He describes the filaments on the body of the larva, and concluded
that they were probably breathing-organs, because of the dark-coloured
vessels within them. These he traced, as we will presently do, to their
union in the stem of the gill, and thence to the air-vessels running
down each side of the body of the larva. He fed them on leaves of the
Water Soldier, and kept them through the winter. In the following June
he found them preparing to undergo their transformation into the pupal
stage, and at the end of the month the moths came out. He was gratified
by seeing the congress of these insects. The females deposited their
eggs on the floating vegetation and on the sides of his aquarium, a
little below the surface of the water, and in about eight days the
young larvae were seen.
[Illustration: FIG. 82.--Larva of _Paraponyx
stratiotata_ (enlarged).]
These larvae must be very abundant, though they do not seem to be often
taken by collectors. In describing an allied (American) species, which
is found on Vallisneria and pondweed, Mr. Hart says[65], ‘They feed
at first exposed on the leaf, but later two or even three leaves are
loosely webbed together, face to face, by each larva, between which it
remains concealed while feeding. They are, therefore, hard to discover
unless their hiding-places are broken up by seining, or the like, when
the larvae may be seen swimming about.’ This is, no doubt, the reason
why these larvae are not more often taken. Anything like a seine net is
of course out of the question for us; but masses of vegetation may be
readily broken up by vigorously working the bottle and net backwards
and forwards amongst them. Specimens I have seen were taken among
duckweed; and Mr. Hart mentions one instance of part of the larval case
being constructed of ivy-leaved duckweed, ‘which was abundant there at
that time.’
Now let us bring our lens to bear, so that we may make out the external
structure, and recognize the similarity of the breathing-organs of this
Moth-larva to those of the Crane-fly larva already treated of (p. 168).
In order to make out the scheme of the gills, which is somewhat
complicated, one should first of all distinguish the spiracles,
remembering that they are not functional. And it is best to begin with
those on the middle segments of the body. They may be detected as
little dark spots, sometimes enclosed in a ring. The head, the first
segment of the thorax, and the last segment of the body, bear no gills;
the second segment of the thorax has but two pairs on each side; and
there is but a single gill on each side of the ninth segment of the
body. On the other (nine) body-segments there are the full number
of five gills on each side, arranged two above, and three below the
spiracle. The upper pair are called supra-stigmals, or gills which lie
_above_ the spiracles; the lower pair are called infra-stigmals,
or gills which lie _below_ the spiracles; and the single one, the
lowest, is known as the pedal or foot gill. These technicalities need
not give us any trouble here, in our examination of the larva; nor do
they present any real difficulty. But it is worth while to master the
arrangement as soon as we get hold of one of these larvae, and then we
shall be able to take up and understand technical descriptions of this
aquatic caterpillar and its allies, in so far, at least, as they refer
to the breathing apparatus.
The gills differ in their character: some few are simple, while most of
them are more or less branched. In Limnobia the branching of the gills
is into a simple fork; in Paraponyx this kind of division also occurs,
and in others most of the gill branches are also given off from the
main stem below one of the branches of the fork.
In Fig. 84 we have a representation of one of these branched gills.
It will not be difficult for us to make out the details as there
shown. But the vessels that run down into the filaments, constituting
them breathing-organs, are smaller than those of Limnobia, and will
consequently require a little more care and patience before we can
distinguish them.
[Illustration:
+---------------+
| GILL GILL |
| SPIRACLE |
| GILL GILL |
| GILL |
+---------------+
FIG. 83.--Diagram of segment of Paraponyx, showing
arrangements of tracheal gills.]
[Illustration:
FIG. 84.--Gill of Paraponyx larva. _a_, _b_,
stem; _c_, _d_, _e_, _f_, branches;
_g_, attachment of the air-vessel of the gill to the main
tracheae of the body. (After De Geer.)]
One would think that, with such an array of gills, this larva ought
to be in good case for its air-supply. It may, perhaps, be doubted
whether this is so. At any rate, the creature adopts the same plan as
the larva of Chironomus, which has no gills at all, for driving away
from its case water that has parted with its oxygen. Water charged with
oxygen pours into the case, and so the air-supply is renewed. This plan
is nothing more than keeping the fore-part of the body in undulating
motion, the tail in both the larvae serving as a point of attachment.
One or two that I have kept made their cases against the side of the
bottle, and so afforded an excellent opportunity of seeing them in this
motion. The Tanypus larva does the same thing. Against the side of one
of my small aquaria a Tanypus larva and a Chironomus larva have both
made tubes; and as I look up from writing these lines I can see them
both hard at this work.
The larva of the Alder-fly (_Si´alis luta´rius_) is also furnished
with tracheal gills, seven on each side. So little is known of the
life-histories of common insects that it may be profitable to introduce
the account of an observer who watched the deposition of the eggs and
the emergence of the young larvae:
‘On April 25 I found, on the rushes round the margin of a small pond,
a great many patches of eggs, and shortly after observed many of the
_Sialis lutarius_ depositing them.
‘They form large patches of from two to three inches in length,
generally encircling the whole rush near the top, but sometimes
deposited on one side only, and extended to about a line in breadth.
‘I counted 100 in a square line, so that each batch may be fairly
considered to contain from 2,000 to 3,000 eggs; the greater portion of
which must consequently perish either in the egg or larva state; as,
common as the insect is, and widely distributed throughout the country,
we should be perfectly overwhelmed with the swarms of the perfect
insect if such were permitted, when it is considered that round this
one small pond there could not have been less than 100 patches of them.
‘The eggs are of a very singular form, and placed in a slanting
position.
‘The females, while depositing them, appeared perfectly motionless on
the rush, and varied considerably in size, being from five lines to
nearly double that in length. Some parts of the patches of eggs are of
a much lighter colour than the rest.
‘On May 3 I found many of the eggs hatching, the little larvae tumbling
about in great numbers, with their bodies erected like [the larvae of]
the _Staphylinidae_.
‘On putting them into water they swam about with the greatest activity,
wriggling and undulating their bodies about much like a serpent or the
tadpoles, and working their legs at the same time[66].’
The author draws attention to the disproportionately large head of the
larvae, which, however, he did not describe, as he had ‘brought some of
them alive, and some eggs for exhibition.’
Sialis larvae occur in most ponds with muddy bottoms. They may be taken
by scooping up some of the mud in a long-handled spoon--a most useful
instrument for the collector--and washing it, or by throwing in the
drag, and bringing to land a mass of water-weed, roots and all. A few
may generally be detected near the roots. They may be picked up with a
small pair of forceps, or with a brush, and dropped into a bottle; or,
better still, into separate tubes; for they are fierce and voracious,
and, failing other food, by no means indisposed to prey on each other.
Their general appearance, and especially their powerful mandibles, give
them some resemblance to the larvae of a water beetle, for which a
celebrated naturalist not unnaturally took them, when he began to study
them. And this would seem to be the opinion of some mounters, for I
have a slide of the mouth parts of this larvae, labelled ‘Mouth parts
of the larvae of a water beetle.’ It was not till I had broken up a
good many Sialis larvae that I found out what the slide really was.
These larvae may be kept alive in small bottles of water, if they
are supplied with food. They will eat Chironomus larvae and those of
Tanypus. Professor Miall has found that they will eat caddis-worms and
May-fly larvae. Probably, no small aquatic creatures that they can
overcome are safe from them.
A larva that is full-fed, and ready to change to become a pupa, will
measure about an inch in length or a little more (Fig. 85). The general
colour is brownish, with dark markings. The legs are powerful, and our
lens will show us that they end in two strong curved claws. From each
of the first seven segments of the abdomen are given off a pair of
jointed tracheal gills or breathing-organs, which are directed upwards
and backwards when the larva is at rest--a rare occurrence--but which
wave to and fro in the water when the creature is swimming.
From this fact has arisen the statement found in most books that the
larva uses these gills not only for respiration, but for locomotion.
Professor Miall has come to a contrary conclusion, and, as he has
kindly informed me, is confirmed in his opinion by the weakness of the
muscles.
[Illustration:
FIG. 85.--Larva of Sialis (enlarged).]
It will be well to make repeated observations till we are satisfied
on the subject. When these larvae are kept, the conditions necessary
to provide them with food and to keep the water aërated by means of
growing vegetation are unfavourable to close observation. It will,
therefore, be necessary to remove one or more of these larvae to a
bottle in which there is nothing but pure water.
The work is now rendered much easier. There is nothing to obstruct. As
soon as the larvae reach the bottom they will walk round and round,
giving us a good opportunity of watching them. In swimming--which may
be backwards as well as forwards--the abdomen is waved from side to
side. To see the backward motion one need only put a dipping-tube or a
pencil, or the like, in front of the larva, so as to bar its progress.
The creature will retreat a step or two, and then, with a flourish of
the abdomen, dart back through the water. The larva will sometimes wave
the abdomen up and down, just as one may see a Chironomus larva do when
it has affixed its dwelling to the side of the glass, and this motion
probably assists the process of respiration.
When the larvae have been watched under the conditions above described,
I have never been able to detect independent motion of the gills. But
it is better that every one should observe for himself, and draw his
own conclusions from what he sees.
Now let us examine a specimen more closely with the lens, or under the
dissecting microscope. The mouth parts may be broken up separately, or
a little careful manipulation will enable us to see the chief features
without injuring the specimen. The head is strong and massive, and
the group of ocelli, or simple eyes, may be clearly made out. The
antennae bear a small pencil of hairs, no doubt sensory in function,
at the extremity, but careful management of the light will be required
to distinguish them. The mandibles are extremely business-like
instruments, and each bears two strong teeth on the inner side. Next
come the maxillae, with their palps, each of which has an appendage,
while each maxilla carries three strong spines. The labium, with its
palps, and the mentum, with its saw-like notchings, may be plainly seen.
The three segments of the thorax offer no difficulty. The legs are
worth more than a cursory examination from their apparatus of spines
and double fringe of hairs. Nine body-segments succeed to the thorax,
and behind these is a long tail-like organ, which some authors consider
represents a tenth segment.
[Illustration:
_h_ _t_ 1 2 3 4 5 6 7 8 9 tail
-- ----- -- -- -- -- -- -- -- -- -- ------
| | | | | | | |
FIG. 86.--Diagram of Sialis larva, showing arrangement
of gills (represented by vertical lines). _h_, head;
_t_, thorax; 1–9, segments of abdomen.]
The gills are seven on each side, and are given off from the spaces
in front of the first seven segments of the abdomen. Each gill is
five-jointed--an unusual arrangement, for the gills of the larvae of
Limnobia and Gyrinus are without joints. With the half-inch Leitz the
branching tracheal tube in the gill may be seen, as well as the double
fringe of hairs and the long hairs at the extremity. The tail-like
organ, though without joints, bears a close resemblance to the gills.
It has two tracheal tubes running through it, and it is fringed on both
sides with hair. Indeed, Professor Miall, F.R.S., compares it to ‘two
ordinary tracheal gills completely fused together.’ The first glance
will convince the observer that the comparison is just.
[Illustration: FIG. 87.--Pupa of Sialis.]
The pupa (Fig. 87) need not detain us, for the larva undergoes its
transformation in the ground, not in the water, where it could be
watched. But it is interesting to notice that the legs and wings are
enclosed in separate cases, and that the segments of the abdomen bear
spines. These spines are extremely serviceable to the pupa when making
its way out of its cell to emerge as a perfect insect, which is well
known, especially to fishermen, as the Alder-fly. It may be found near
streams, and rarely uses its wings.
_Ptychoptera paludosa_ is a small Crane-fly, with an aquatic larva
which will repay observation. It is one of the group generally called
‘rat-tailed maggots,’ from the peculiar character of the breathing
apparatus, which consists of a retractile tube at the end of the
abdomen. It is, I believe, better known to some dealers than the larva
of the Drone-fly, the rat-tailed maggot of Réaumur. A few months ago I
wanted some Drone-fly larvae, and asked a dealer to supply me. When the
larvae arrived and were turned out for examination, they proved to be
Ptychoptera larvae--which I did not want. I naturally wrote to point
out the mistake; and was told, in reply, that the larvae sent were the
only ‘rat-tails’ known to my correspondent.
This larva is a mud-dweller, and is best captured by scooping up
surface mud near the banks of pools and ditches, just where the water
shallows on to the shore. This should be washed in a small dish or
saucer, so as to carry away the mud and leave the larvae wriggling
on the bottom. They may be picked up with a brush and dropped into a
bottle for transport home.
There is not the slightest difficulty about keeping them for
observation. A bottle of the capacity of six or eight fluid ounces
will make a good aquarium for a dozen or even twenty. The bottom should
be covered to the depth of about an inch with mud fairly rich in
organic matter. My own plan has been to use the accumulation from the
bottom of a large aquarium. In this the larvae will bury the body, and
feed, the tail protruding and thrust up to the surface of the water, of
which there should be about two inches above the mud.
This is a liberal allowance of space. A couple of these larvae lived
with me for some months in a glass capsule two inches in diameter and
three-quarters of an inch in height. The mud at the bottom and the
water covering it together measured about half an inch. Both pupated,
and in due time from the pupa cases a perfect insect came out.
But that larvae may pupate, they require to be well fed. How shall
we know when the bulk of the nourishment has been extracted from the
mud? From the castings of the larvae; and these, though of a different
shape, are as easy to be distinguished as the castings of the earthworm
in the garden or those of the lobworm on the seashore. All the mud that
passes through the bodies of the larvae is discharged in the form of
tiny hard, cylindrical pellets; and when the mass consists of these
pellets it should be changed, or the larvae will go short of food. They
will, however, support long fasts.
From Fig. 88 we may get a good idea of the appearance of the larvae
when kept in confinement. The figures are rather less than natural
size, and all the attitudes were sketched from life. One is seen
extended on the bottom; two are partially buried in the mud, with the
breathing-tube protruding. The larva on the mud, and bent into curves,
is just about to rise to the surface; others are shown in the act of
rising, while one has its breathing-tube raised above the surface, and
another is attached by the breathing-tube to the side of the glass
vessel. The larva with the star-like process at the end of the tail is
that of Odontomyia, a large bee-like fly.
[Illustration: FIG. 88.--Larvae of _Ptychoptera
paludosa_ (from life).]
A larva of good size, like that of Ptychoptera, is especially easy to
examine; and by reason of its transparency the tracheal tubes may be
clearly traced. The under surface of the larva should be first looked
at, and its adaptation for existence in the mud of a pond-bottom will
be evident. The creature is legless, but possesses three pairs of
false legs armed with dark-coloured hooks, and each body-segment bears
a circle of stiff hairs, which enable the larva to travel through
the mud, in the same way that the earthworm moves through the soil.
Moreover, the segments between these circles are pretty thickly set
with hairs.
The tracheal tubes run down on each side of the body, not in a direct
line, for there is a most ingenious arrangement by which contraction
and expansion of the larva, and the protrusion and retraction of
the tail, are provided for. One can easily discern that in most of
the segments the tubes are large, and that these large portions are
connected by smaller tubes, whence others are given off into the body.
These connecting-tubes are loop-like when the larva is of the normal
length, but are straightened out, thus adding to their length, when the
larva is extended.
The opening and closing of these loops may be observed at leisure if
a larva be put in a long excavated slip, with some water, and then
covered with a plain glass slip. The two slips, fastened together with
small elastic bands, should then be laid on the stage of the dissecting
microscope for examination; or they may be held in the hands, and the
movements of the larva watched with the hand lens.
In the posterior segments of the body the tracheal tubes run side by
side, while in the tail itself they are, so to speak, intertwined. When
the tip of the tail pierces the surface-film a fresh supply of air is
taken in.
At the base of the extensile portion are two processes which diverge,
one on each side, at an angle of 45 degrees. These, according to a
German observer, are tracheal gills, and they are absorbed just before
the larva enters the pupal condition.
Réaumur found these larvae plentifully in the Bois de Boulogne, and
gives a figure[67]. He was not, however, successful in rearing the fly.
Lyonnet not only took the larvae and kept them in an aquarium, but
watched their change into the pupal condition, and saw them emerge as
perfect insects. An abstract of this description will probably be of
interest.
[Illustration:
FIG. 89.--_A._ Ptychoptera larva (enlarged).
_B._ Tail, showing air-vessels (still more enlarged).
(After Lyonnet.)]
He tells us that the larvae showed signs of changing into pupae in
June. The change was made without the larvae leaving the water, and
they underwent all their transformations in less than a fortnight.
At the approach of the change the larvae became whiter in colour,
but less transparent. Then they cast their skin, leaving therein the
air-vessels, or rather their external covering. After this last moult
was over, he was surprised to find that the tube which formed the tail
of the larva, and by which it took in a supply of air, though it serves
the same purpose in the pupa, is attached to the thorax, near the top
of the head[68]. Lyonnet appears to have overlooked the fact that there
was a second and shorter tube given off from the thorax, which most
observers consider to be functionless (Fig. 90).
[Illustration: FIG. 90.--Pupa of Ptychoptera. (After
Lyonnet.)]
Strange as is the larva, the pupa is stranger still, and seems even
better adapted for existence in the mud. The hinder part of each
segment of the abdomen is thickened and studded with chitinous
projections. This thickening is more marked, and of greater extent in
each succeeding segment, reaching its greatest development in the last
segment, which is armed with hooks. The body part of each segment bears
rows of smaller spines, so that this pupa should have little or no
difficulty in moving through pretty thick mud.
Several of these Crane-flies have passed through all their stages with
me, and in nearly every case the transformation from pupa to perfect
insect was made in water--in a tube three inches long, with a diameter
of about an inch. The larvae were taken about the middle of September.
My notes show that the first pupated on November 17, and the first fly
came out on November 25.
The long breathing-tube of the pupa was several times purposely
displaced from its position on the surface. The creature was evidently
incommoded, and twisted itself into strong curves; the head was thrown
from side to side till part of the breathing-tube was raised above the
surface and adhered to the side of the glass tube. Nor did the efforts
cease till a considerable portion of the tube was in free communication
with the air. This would seem to show that the air-supply is taken
through the bladders which appear at irregular intervals in the
breathing-tube, and not at the tip, where the keenest observers have
failed to find an opening.
INDEX
Acridiidae, 80.
Alder-fly, larva of, 177;
pupa of, 182.
American Cockroach, 74.
Amphipods, 141;
Rev. T. R. R. Stebbing on, 141.
Aquaria, description of, 20.
Arachnoidea, 96.
_Argyroneta aquatica_, 108;
De Geer on, 109;
nest of, 110.
Arthropods, 27;
divisions of, 28;
description of, 29.
Ascidians, Darwin on, 13.
_Asellus aquaticus_, description of, 153.
Assassin Worm, 158.
Aurivillius, Dr., on Crabs, 150.
Bate and Westwood on Gammarus, 147;
on Talitrus, 151.
Bateman, Rev. G. C., on Hydrophilus, 50;
on Nepa, 91;
on China Marks, 171.
Beakers, 21.
Beetle Mite, 119.
Belt on Blatta, 67.
Black Beetle, 63.
Black-bobs, 64.
Blackwall on Spiders, 101, 102.
_Blatta orientalis_, description of, 63, 66;
Gilbert White on, 64;
Dr. Sharp on, 65;
Belt on, 67;
Sir J. Lubbock on, 68;
anatomy of, 68;
breathing of, 70;
Swammerdam on, 74;
Professor Plateau on, 74.
Book Scorpions, 96.
_Brachelytra_, 59.
Broad-clawed Porcelain Crab, 139.
Brown China Mark, 172.
Brushes, 23.
Bugs, 86.
Burgess, Mr., on larva of Dytiscus, 160.
Butler, Dr., on Spiders, 100.
Butler, Mr. E. A., on Forficula, 79.
Capsules, 21.
_Carcinus maenas_, description of, 136.
Centipedes, 122;
marine, 125.
Cerci, 47.
Chelate, meaning of word, 132 _n._
China Marks, 171;
Rev. G. C. Bateman on, 171;
De Geer on, 172.
Cockroach, 63.
Cocktail Beetle, 57.
Coleoptera, 32.
Collecting, method of, 25.
Corixa, 94;
Graber on, 95;
Sir J. Lubbock on, 95.
Crab, Shore, 136;
Porcelain, 139.
Crane-fly, 165.
Crustacea, 128.
Daddy-longlegs, 103.
Dallas on Ocypus, 61.
Darwin on microscopes, 12;
on Ascidians, 13.
Devil’s Coach Horse, 57.
Dipping-tubes, 23.
Dissecting microscope, 18.
Dissection, mode of, 37.
Diving Spiders, 108.
Dugès on Water Mites, 117.
Dung Beetle, 119.
_Dytiscus marginalis_, 31;
etymology of, 33 _n._;
breaking of shells by, 33;
Sowerby on, 34;
description of, 35;
food of, 36;
anatomy of, 37;
habits of, 41;
Kirby on, 41;
Sir J. Lubbock on, 42;
Professors Lowne and Miall on, 45;
Dr. Sharp on, 47;
abdomen of, 47;
breathing of, 48;
larva of, 157;
Swammerdam on, 158, 159;
Mr. Burgess on, 160.
Earwig, 75.
Edriophthalma, 129.
Elytra, 41.
_Epeira diadema_, description of, 98;
web of, 98;
J. A. Thomson on, 100;
Dr. Butler on, 100;
Blackwall on, 101, 102;
mode of taking its prey, 102;
Hudson on, 103;
feet of, 104;
spinnerets of, 105.
Evans, W., on Sialis, 177.
_Field_, the, quoted, 33, 35.
Forceps, 22.
_Forficula auricularia_, 75;
Kirby and Spence on, 76;
De Geer on, 76;
young of, 76;
forceps of, 77;
anatomy of, 77;
Butler on, 79;
Dr. Sharp on, 79.
Formalin, 24.
Forty-legs, 122.
Fresh-water Shrimp, 142.
_Gamasus coleoptratorum_, 119.
_Gammarus marinus_, 146;
Dr. J. Salter on, 147.
_Gammarus pulex_, 142;
anatomy of, 144.
Geer, De, on Forficula, 76;
on Locusta, 80;
on Water Mites, 116;
on Beetle Mites, 120;
on Lithobius, 123;
on Julus, 126;
on larva of Limnobia, 167;
on Paraponyx, 172.
Geophilus, 124.
_Geophilus crassipes_, 125;
Mr. Pocock on, 125.
Glass block, 22.
Glass box, 22.
Glass slips, 22.
Gosse on Prawns, 133.
Graber on Corixa, 95.
Grasshopper, Great Green, 80.
Great Water Beetle, 49.
Hart, Mr., on Paraponyx, 173.
Harvestmen, 96.
Hemiptera, 86.
Hill, Dr., on Nepa, 90.
Hudson on Spiders, 103.
Hundred-legs, 122.
Hunting Spiders, 98.
Hydrachna, 113.
_Hydrachna globula_, 118 _n._
Hydrophilus, larva of, 164;
Lyonnet on, 164.
_Hydrophilus piceus_, 49;
Bateman on, 50;
legs of, 53;
Simmermacher on, 53;
breathing of, 54;
cocoons of, 54;
Lyonnet on, 54.
Hymenoptera, wings of, 170.
Idotea, 143.
_Idotea pelagica_, 155.
Illinois State Laboratory, mode of collecting in, 25.
‘Insects,’ 27;
divisions of, 32.
Invertebrates, 28.
Isopods, 152.
Julus, 121, 124.
_Julus terrestris_, 126;
De Geer on, 126;
Dr. Sharp on, 126.
Jumping Spiders, 105.
Kew, Mr., on dispersal of shells, 130.
Kirby on Dytiscus, 41;
on Ocypus, 59;
on Forficula, 76;
on Locusta, 83;
on insect noises, 84;
on Salticus, 107.
Knives, 24.
Land Bugs, 86.
Leaping Orthoptera, 79.
Leitz, lenses of, 16.
Lichtenstein on Locusta, 83.
Limnaea broken by Dytiscus, 33.
_Limnobia replicata_, larva of, 165;
De Geer on, 167;
pupa of, 168.
_Lithobius forficatus_, 122;
De Geer on, 123;
Dr. Sharp on, 123.
_Locusta viridissima_, 80;
Dr. Sharp on, 80, 85;
De Geer on, 80, 83;
Westwood on, 81;
Kirby on, 83;
Lichtenstein on, 83;
ear of, 85.
Locustidae, 80.
Lowne, Professor, on Dytiscus, 45.
Lubbock, Sir J., on Dytiscus, 42;
on Blatta, 68;
on Corixa, 95;
on Opossum Shrimp, 135.
Lyonnet on larva of Hydrophilus, 164;
on Ptychoptera, 186.
Magnification, power of, 15 _n._
Mainland, Mr. G. E., on Water Mites, 118.
Malacostraca, 128;
Rev. T. R. R. Stebbing on, 128.
Margined Water Beetle, 31.
Masking Crabs, 150.
_Melicerta janus_, 150.
Miall, Professor, on Dytiscus, 45;
on Sialis larvae, 179, 181.
Microscopes, use of, 11;
description of, 15.
Millepedes, 121, 125.
Mites, description of, 112.
Model, a calico, 30.
Myriapods, 96, 120.
Mysis, 135.
_Nature Notes_ on Millepedes, 121.
Needles, 23.
_Nepa cinerea_, 86;
mode of keeping, 88;
Swammerdam on, 89;
Dr. Hill on, 90;
Rev. G. C. Bateman on, 91;
anatomy of, 91.
Noises made by insects, 84.
_Notonecta glauca_, 93.
_Ocypus olens_, 57;
Kirby on, 59;
as a pet, 59;
Dallas on, 61;
larva of, 61.
Opossum Shrimp, 135;
Sir J. Lubbock on, 135.
_Orchestia littorea_, 151.
Orthoptera, 63.
Ovipositors, 82.
_Palaemon serratus_, 129.
_Palaemonetes varians_, 130.
_Paraponyx stratiotata_, 171;
De Geer on, 172;
Mr. Hart on, 173;
anatomy of, 174.
Peripatus, 30;
Professor Sedgwick on, 31.
_Periplaneta americana_, 74.
Pholcus, 103.
Phylum, definition of, 27.
Planorbis broken by Dytiscus, 33.
Plateau, Professor, on Blatta, 74.
Pocket lens, description of, 13.
Pocock, Mr., on Geophilus, 125.
Podophthalma, 129.
_Porcellana platycheles_, 139.
Prawns, 129;
Gosse on, 133;
Sowerby on, 133.
Ptychoptera, larva of, 182;
pupa of, 187;
Réaumur on, 185;
Lyonnet on, 186.
Quekett Microscopical Club, incident at, 20.
‘Rat-tails,’ 182.
Réaumur on Ptychoptera, 185.
Robertson, Mr., on Talitrus, 151.
Salter, Dr. J., on Gammarus, 147.
_Salticus scenicus_, 105;
Kirby and Spence on, 107;
foot of, 108.
Sand-hopper, 151.
Scorpions, 96.
Sedgwick, Professor, on Peripatus, 31.
Sharp, Dr., on Dytiscus, 47;
on Blatta, 65;
on Forficula, 79;
on Locusta, 80, 85;
on Lithobius, 123;
on Julus, 126;
on wings of Hymenoptera, 170.
Shells broken by Dytiscus, 33;
Mr. Kew on dispersal of, 130.
Shore Crab, 136.
Shore-hopper, 151.
Shrimp, 132.
_Sialis lutarius_, larva of, 177;
W. Evans on, 177;
anatomy of, 180;
pupa of, 182.
Sicarius, 158.
Simmermacher on Hydrophilus, 53.
Sirex, 82.
Sowerby, G. B., on Dytiscus, 34.
Sphaerium, 130.
Sphaeroma, 155.
Spiders, general description of, 96;
Trap-door, 97;
Hunting, 98;
Garden, 98;
Jumping, 105;
Diving, 108.
Stebbing, Rev. T. R. R., on etymology of Dytiscus, 33 _n._;
on Malacostraca, 128;
on meaning of _chelate_ and _sub-chelate_, 132 _n._;
on Amphipods, 141.
Stewart, Professor, incident of, 20.
Stilopyga, 63.
Swammerdam on Blatta, 74;
on Nepa, 89;
on Water Mites, 114;
on Woodlice, 156;
on Dytiscus larva, 158, 159.
Tailed Wasp, 82.
_Talitrus locusta_, 151;
Bate and Westwood on, 151;
Mr. Robertson on, 152.
Tanypus, larva of, 176.
Tegetmeier, Mr. W. B., on destruction of shells, 34.
Thomson, J. A., on Spiders, 100.
Trap-door Spider, 97.
Vertebrates, 28.
Wart-eater, 81.
Water Beetle, Margined, 31;
the Great, 49.
Water Boatman, 93.
Water Bugs, 86.
Water-devil, 157.
Water Mites, 113;
Swammerdam on, 114;
De Geer on, 116;
Dugès on, 117;
Mainland on, 118.
Water Scorpion, 86.
Water-tiger, 157.
Westwood on Locusta, 81.
White, Gilbert, on Blatta, 64.
Wing-cases, 41.
Wireworm, 126.
Wood, Rev. J. G., on lens stand, 15.
Woodlice, 155;
Swammerdam on, 156.
Worms, 29.
Wright, Mr. L., on microscopes, 16.
Zeiss, lenses of, 15.
THE END.
FOOTNOTES:
[1] Darwin, _Descent of Man_ (2nd ed.), p. 159, note 23.
[2] The power of magnification of a lens is the ratio of its focal
distance to 10 inches. Thus a lens of 1 inch focus (or focal distance)
magnifies 10 times (written × 10, or ten diameters); one of ½ in. focal
distance, 20 times, and so on.
[3] _A Popular Handbook to the Microscope_, p. 39.
[4] _Journal of the Quekett Microscopical Club_, v. 148.
[5] _Ponds and Rock Pools_, p. 17.
[6] _Bulletin of the Illinois State Laboratory of Natural
History_, iv. 158.
[7] ‘Dytiscus’ is written of set purpose. It is not, as some people
tell us, a miswriting for Dyticus; but a properly formed diminutive,
from the Greek _dutēs_ = a diver; like _paidiskos_ = a little boy.
Linnaeus consistently calls the genus Dytiscus from 1735 onwards.
Dyticus only dates from Geoffroy’s _Histoire Abrégée des Insectes_,
first published anonymously in 1762. On this question of nomenclature I
am glad to have the support of the Rev. T. R. R. Stebbing, F.R.S., who,
in answer to my inquiries, kindly wrote, ‘Darwin uses “Dytiscus” in the
_Origin of Species_, and I should decidedly recommend its being upheld.’
[8] April 4, 1896.
[9] _Popular History of the Aquarium_, p. 258.
[10] May 2, 1896.
[11] International Science Series, No. lxv.
[12] _Aquatic Insects_, pp. 55, 56.
[13] _Zeitschrift f. wiss. Zoologie_, Bd. xl. S. 481.
[14] _Mémoires du Muséum d’histoire naturelle_, xviii. 454 sqq.
[15] I have purposely given _Blatta_ as the generic name, rather
than _Stilopyga_, which should properly be used, as the former is
only employed in very recent literature.
[16] Miall and Denny, _The Cockroach_, p. 20.
[17] _Cambridge Natural History_, v. 231.
[18] _The Senses of Animals_, p. 44.
[19] _Cambridge Nat. Hist._ v. 223.
[20] _Book of Nature_, p. 94.
[21] This refers to the gizzard. _Echinus_ was used to denote the
third stomach of Ruminants (now called the manyplies), because it was
thought to resemble a hedgehog rolled up.
[22] Miall and Denny, _The Cockroach_, p. 118 (note).
[23] _Introduction to Entomology_, letter xi.
[24] _Proceedings of the Zoological Society_, 1892, p. 586.
[25] _Our Household Insects_, pp. 159–163.
[26] Kirby and Spence, _Introd. to Entomology_, ed. 1870, p. 484.
[27] _Cambridge Natural History_, v. 318.
[28] _The Senses of Animals_, p. 75.
[29] J. Arthur Thomson, _Outlines of Zoology_, p. 288.
[30] _Science for All_, ii. 178.
[31] _British Spiders_, p. 10.
[32] _British Spiders_, p. 359.
[33] _Naturalist in La Plata_, p. 188.
[34] _Mémoires_, vii. p. 304 sqq.
[35] _Book of Nature_, pp. 101, 102.
[36] _Mémoires_, vii. 144, 145.
[37] The specimen was kindly identified for me, by Dr. Trouessart of
Paris, as a nymph of _Hydrachna globula_ (Dugès), and has been
deposited in the British Museum (Natural History).
[38] _Mémoires_, vii. 123–128.
[39] _Cambridge Natural History_, vol. v. ch. ii.
[40] _Nature_, Dec. 12, 1895.
[41] _Mémoires_, vii. 569.
[42] _Crustacea_, p. 7.
[43] _Crustacea_, p. 225.
[44] International Science Series, No. lxxv.
[45] ‘A limb is _chelate_ when it has joints that will act
together like a pair of tongs. Generally this character is produced by
the hinging of the seventh joint a considerable way down on the side
of the sixth. When the seventh joint, or finger, can be folded back
upon the sixth, although the latter is not produced into any thumb-like
process to oppose it, the limb is then said to be _sub-chelate_,
the claw being in that case partial, though often extremely efficient.’
Stebbing, _Crustacea_ (International Science Series, lxxiv), p. 45.
[46] _Popular History of the Aquarium_, p. 223.
[47] Lubbock, _Senses of Animals_ (International Science Series,
lxv.), p. 93.
[48] _Aquarium_ (ed. 1856), pp. 41, 42.
[49] _Crustacea_ (International Science Series, lxxiv), pp. 8, 9.
[50] Bate and Westwood, _British Sessile-eyed Crustacea_, i. 8.
[51] _Trans. Connecticut Academy_ (1882), iv. 274, 275, note.
[52] _Ponds and Rock Pools_, p. 118.
[53] _British Sessile-eyed Crustacea_, i. 21.
[54] _Proceedings Nat. Hist. Soc. Glasgow_, vol. i. pt. ii. n. s.
pp. 130–132.
[55] _British Sessile-eyed Crustacea_, ii. 381.
[56] _Book of Nature_, i. 174.
[57] _Mémoires_, iv. 386.
[58] _Proceedings Boston Society of Natural History_, xxi. 223–228.
[59] _Natural History of Aquatic Insects_, p. 47.
[60] _Mémoires du Museum_, xviii. 442, 443.
[61] _Mémoires_, vi. 352–55.
[62] _Diptera_, iii. 281.
[63] _Cambridge Natural History_, v. 494.
[64] _Mémoires pour servir_, i. 577 sqq.
[65] _Bulletin of the Illinois State Laboratory of Natural
History_, iv. 167.
[66] W. Evans, _Trans. Entomol. Soc._ (London), iv. 261.
[67] _Mémoires pour servir_, t. vi. Plate 31.
[68] _Mémoires du Muséum_, t. xix. pp. 103, 104.
Transcriber’s Notes:
1. Obvious printers’, punctuation and spelling errors have been
corrected silently.
2. Some hyphenated and non-hyphenated versions of the same words have
been retained as in the original.
3. Superscripts are represented using the caret character, e.g. D^r.
or X^{xx}.
4. Italics are shown as _xxx_.