Guide to the study of insects, and a treatise on those injurious and beneficial to crops: for the use of colleges, farm-schools, and agriculturists online

elongated muscular parts inclosing the penis (70. From Newport.

FIG. 54. Female organs of generation of Athalia centifolice. a, 6, c,the eighteen
ovarial tubes originating from each of the two oviducts (e), and containing the im-
mature eggs;/, the spcrmatheca; g, poison-sac, the poison being secreted in the
secretory vessels h. The poison flows through the oviduct into the sting and thence
into the wound made by the sting. 10, the terminal ganglia of the nervous cord.
From Newport.




ORGANS OF GENERATION. 45

of the oviduct arc from one to five appendages, the most impor-
t.-uit of which is tin- xjH'ftnatheca (the others being sebaceous
glands), which receives the fertilizing fluid of the male during
sexual union, and in which, according to Darwin, the male ele-
ment "is enabled to keep alive four or five years."

Insects bisexnnl. With the exception of the Tardigrades,
which are doubtfully referred to the Mites (Acarina), there are
no hermaphrodites among Insects, that is, there are no individ-
uals having both male and female organs, and capable of self-
impregnation. On the contrary, the sexes are distinct ; Insects
are bisexual.

Hermaphrodites, so-called. Cases not unfrequently occur in
which from arrest of development of the embryo, the sexual
organs are imperfectly developed, so as to present the appear-
ance of being both male and female. "Siebold has investigated
some hermaphrodite Honey-bees belonging to the Italian race,
obtained from a Dzierzon hive at Constance. He found in
many of them a combination of sexual characters, not only in the
external parts, but also in the generative organs. The mixture
of the external characters is manifested sometimes only in the
anterior or posterior part of the body, sometimes in all parts
of the body, or only in a few organs. Some specimens pre-
sent male and worker characters on the two sides of the body.
The development of the internal organs is singularly correla-
ted with these peculiarities of external organization. The sting,
with its vesicle and gland, is well developed in hermaphrodites
with the abdomen of the worker ; soft in those with the drone-
abdomen. The seminal receptacle, when present, is empty.
The ovaries contain no ova. In the hermaphrodites with the
drone-abdomen, the male sexual organs are well developed, and
the testes contain spermatozoids. Frequently with testicular
and ovarian organs present on each side, the epididymis and
copulatory apparatus are well developed, and an imperfect
poison-apparatus exists. In these cases the tube contains
spermatozoids, but there are no ova in the ovaries. The her-
maphrodites are thrown out of the cell by the workers as soon
as they emerge, and speedily perish. Siebold ascribes the pro-
duction of these hermaphrodites to an imperfect fecundation
of the ovum." (Zeitschrift fur Wissenschaftliche Zoologie,
1864, p. 73. See Giintker's Zoological Review for 1864.)



46 THE CLASS OF INSECTS.

Mr. Dunning describes a specimen of Fidonia piniaria,
"which was sexually a female, and the abdomen was appar-
ently distended with eggs ; the general color was midway be-
tween the colors of the ordinary male and female, but the size
and markings were those of the male. (Transactions Ento-
mological Society, London, Aug. 7, 1865.) Professor West-
wood states that "he had an Orange-tip Butterfly (Anthocharis
cardamines) , which was female in every respect, except that
on the tip of one fore- wing were about a dozen of the bright
orange scales which characterize the male."

THE EGG. Professor H. J. Clark (Mind in Nature) defines
an egg to be a globule surrounded by the vitelline membrane,
or yelk-envelope, which is protected by the chorion, or egg-
shell, consisting of "two kinds of fluid, albumen and o7, which
are always situated at opposite sides or poles." "In the earli-
est stages of all eggs, these two poles shade off into each
other," but in the perfectly developed egg the small, or albu-
minous pole, is surrounded by a membrane, and forms the
Purkinjean (germinal) vesicle ; and thirdly and last, the inner-
most of the three globules is developed. This last is the
Wagnerian vesicle, or germinal dot. The oily matter forms the
yolk. Thus formed, the egg is the initial animal. It becomes
an animal after contact with the male germs (unless the product
of organic reproduction), and the egg-shell or chorion is to be
considered as a protection to the animal, and is thrown off
when the embryo is hatched, just as the larva throws off its
skin to transform into the pupa. So that the egg-state is
equivalent to the larva state, and hence there are four stages
in the life of an insect, i. e. the egg, the larva, the pupa, and
the imago, or adult state.

The egg is not always laid as a perfect egg (Clark). It
sometimes, as in the Ants, continues to grow after it is laid by
the parent, like those of frogs, which, according to Clark, "Are
laid before they can hardly be said to have become fully formed
as eggs." Again, others are laid some time after the embryo
has begun to form ; and in some, such as Melophagus and
'Braula, the larva is fully formed before it is expelled from the
oviduct.




THE EGG. 47

Eggs arc usually small in proportion to the size of the
parent; but in many minute forms (i.e. Pulex, Pediculus, etc.)
they are proportionately much larger. In shape eggs are
either spherical or oblong. In some there are radiating append-
ages at one end, as in those of Nepa and lianatra ; or they are
provided with a single stalk, as in Chrysopa, Cynips, and
Ophion.

The eggs of most Hymenoptera, Diptera, and many Coleop-
tera are usually cylindrical ; those of Lepidoptera are more
generally spherical. The eggs of the Mosquito are laid in a
boat-shaped mass, which floats on the surface of quiet pools,
while those of the Chrysopa, or Lace-winged Fly (Fig. 55), are
supported on long pedicels.
They are almost invariably
laid near or upon objects des-
tined to be the food of the Fig. 55.
future larva. Thus the Copris, or "Tumble-bug," places its
egg in a ball of dung which it rolls away to a secure place ;
the Flesh-fly oviposits on meat ; and all vegetable-feeders lay
their eggs on the food-plant where the larva, upon its exit
from the egg, shall readily find an ample supply of food.

The posterior end of the egg is more often the fixed one, and
it may thus be distinguished from the anterior pole. In the
eggs of some Diptera and Orthoptera. the ventral side of the
embryo, according to Gerstaecker, corresponds to the convex
side of the egg, and the concave side of the latter corresponds
to the dorsal region of the embryo.

The surface of the chorion, or egg-shell, which is dense and
brittle, is often covered by a mosaic- work of more or less regu-
lar facets. In many small eggs the surface is only minutely
granulated, or ornamented with ribs and furrows, as in those
of many Butterflies.

The Micropyle. On the anterior end (though sometimes
at both ends) of the egg is one or more pores of exceeding
minuteness, through which the spermatozoa (more than one
of which, according to Darwin, is requisite to fertilize an
ovule) enter to fertilize the egg-contents. In some cases
these micropyles are scattered over the whole surface of the egg.
Fig. 5Ga represents the micropyles of Nepa cinerea, consisting







48 THE CLASS OF INSECTS.

of a whorl of long bristles. Those of Locusta viridissima (Fig.
566) slightly resemble toadstools. Fig. 56 c represents the an-
terior pole of the egg with
the micropyles of Pyrliocoris
apterus. {From Gerstaecker. )
This contact of a male
sperm-cell with the yolk is
the fertilization of the egg.
From this moment begins the
life of the embryo. Fertiliza-
tion of the female germ by
56 - means of the male sperm,

through the congress of the sexes, is the rule with bisexual
animals, but there are exceptions among insects. An embryo
may start into being without the interposition of the male ; to
this mode of generation has been applied by Leuckart the term
Parthenogenesis. Among certain species of insects there are
some individuals which, by a sort of budding process, and with-
out the aid of the male element, throw off summer broods, con-
sisting of "asexual" individuals, which, as winter approaches,
are succeeded by a brood of true males and females, the latter
of which lay eggs. This phenomenon, called by Steenstrup
''alternation of generations," has been observed among a com-
paratively few species, and the apparent design of such an
anomalous mode of reproduction is to afford an immense num-
ber of individuals, thus providing for the continuance of the
species. The individuals in whom this budding process takes
place are called "asexual" because, though they may resemble
the female sex outwardly, their sexual organs are only partially
developed. This budding process is the same in kind with that
observable in the Jelly-fish, which throw off by parthenogen-
esis, or alternations of generations, summer broods of immense
extent, but in winter propagate by true eggs. Huxley has
studied the development of Aphis by parthenogenesis, the
anomalous nature of which has previously been discovered by
Bonnet, Trembly, Lyonet, Degeer, Kyber, and others, and
arrives at the following conclusions :

"1. Ova deposited by impregnated female Aphides in autumn
are hatched in the spring.



ALTERNATION OF GENERATIONS. 49

2. From these ova viviparous, and, in the great majority of
cases, apterous forms proceed.

3. The broods to which these give rise are either winged or
apterous, or both.

4. The number of successive broods has no certain limit, but
is, so far as we know at present, controlled only by tempera-
ture and the supply of food.

5. On the setting in of cold weather, or in some cases on the
failure of nourishment, the weather being still warm, males
and oviparous females are produced.

6. The males may be either winged or apterous.

7. So far as I am aware, there is no proof of the existence
of any exception to the law that the oviparous female is apte-
rous.

8. Viviparous Aphides may hybernate, and may co-exist with
oviparous females of the same species." (Linnsean Transac-
tions, xxii, p. 198.)

The origin of the viviparous, asexual, or agamic (from the
Greek a, without ; game, marriage) individual, as it may be
more properly called, is, up to a certain stage, the same as
that of the true egg, i.e. until the germ (pseudovum) of
the former is detached from the false ovary (pseudovarium).
"From this point onwards, however, the fate of the pseudovum
is different from that of the ovum. The former begins at once
to be converted into the germ ; the latter accumulates yelk-sub-
stance, and changes but little. Both bodies acquire their mem-
branous investment rather late ; within it the pseudovum
becomes a living larva, while the ovum is impregnated, laid,
and remains in a state of rest for a longer or shorter period.

''Although, then, the pseudovum and the ovum of Aphis
are exceedingly similar in structure for some time after they
have passed out of the condition of indifferent tissue, it cannot
be said that the sole difference between them is, that the one
requires fecundation and the other not. When the ovum is of
the size of a pseudovum which is about to develop into an em-
bryo, and, therefore, long before fecundation, it manifests its
inherent physiological distinctness by becoming, not an em-
bryo, but an ovum. Up to this period the influence of fecunda-
tion has not been felt ; and the production of ova, instead of
4



50



THE CLASS OF INSECTS.



pseudova, must depend upon a something impressed upon the
constitution of the parent before it was brought forth by its
viviparous progenetrix." (Huxley.)

Siebold has also shown that the "ova of the Queen-bee pro-
duces females or males, according as they are fecundated or
not. The fecundated ovum produces a queen or a neuter
according to the food of the larva and the other conditions to
which it is subjected ; the unfecundated ovum produces a
drone." This is analogous to the agamic reproduction of
Aphis, and "demonstrates still more clearly the impossi-
bility of drawing any absolute line of demarcation histologi-
cally between ova and buds."

This process of reproduction is not known in the Myriapods.
It occurs among the mites (Acarina), and occurs in isolated
genera of Hemiptera (Aphis, Chermes, Lecanium, and Aspidi-
otus according to Gerstaecker).

Among Lepidoptera the Silk-moth sometimes lays fertile
eggs without previous sexual union. This very rarely hap-
pens, for M. Jourdain found that, out of about 58,000 eggs
laid by unimpregnated silk-moths, many passed through their
early embryonic stages, showing that they were capable of
self-development, but only twenty-nine out of the whole
number produced caterpillars. (Darwin.) Several other moths *
have been found to lay fertile eggs without previous sexual
union, and among Hymenoptera, Nematus ventricosus, Cynips,
Neuroterus, perhaps Apophyllus (according to Gerstaecker),
and Cynips spongifica (according to Walsh, Proceedings of

*We give a list from Gerstaecker (Bronn's Classen und Ordnungen des Thier-
reichs) of all the known cases of agamic reproduction in this suborder, with the
number of times the phenomenon has been observed, and the names of the ob-
servers.

Gastropacha quercus, once (Plieninger).

Liparis dispar, once (Carlier).

" Eager moth" (? Liparis dispar), (Tardy,

Westwood).

Liparis ochropoda, once (Popoff).
Orgyia pudibiinda, once (Werneburg).
Psyche apiformis, once (Rossi).

" helix (Siebold).
Solenobia lichenella (Siebold).

" triquetrella (Siebold).
Bombyx mori, several times.



Sphinx ligustri, once (Treviranus).
Smerinthus populi, four times (Nord-

mann).

Smerinthus ocellatus, once (Johnston).
Euprepia caja, five times (Brown, etc.).

" mllica, once (Stowell).
Telea Polyphemus, twice (Curtis).
Gastropacha pint, three times (Scopoli,

etc).

Gastropacha quercifolia, once (Basler).
potatoria, once (Burmeis-
ter).

The subject has been also discussed by Siebold in his work entitled, A true Par-
thenogenesis in Lepidoptera and Bees; by Owen, in his "Parthenogenesis," and
by Sir J. Lubbock in the Philosophical Transactions, London, vol. 147, pt. 1.




ALTERNATION OF GENERATIONS. 51

the Entomological Society of Philadelphia) . Parthenogenesis,
or agamic reproduction, is, then, the result of a budding pro-
cess, or cell-growth. This process is a common mode among
the Radiates, the low Worms, and the Crustaceans. Metamor-
phosis is simply a series of marked stages, or periods, of
growth ; and hence growth, metamorphosis, and agamic re-
production are morphologically identical. All animals, there-
fore, as well as plants, grow by the multiplication of cells.

After hearing the surprising revelations of Bonnet, Reaumur,
Owen, Burnett, and Huxley on the asexual mode of generation
in the Aphis, we are called to notice still a new phase of repro-
duction. None of the observers just mentioned were accus-
tomed to consider the virgin aphis as immature, but rather as
a wingless adult Plant-louse. But Nicolas Wagner, Professor
of Zoology at Kasan,* supported by able vouchers for the
truth of his assertions, both in Russia and in Germany, who
have repeated and thoroughly tested his observations, has
observed an asexual reproduction in the larva of a Cecidomy-
ian fly, Miastor metraloas Meinert, and Meinert has observed
it in this species and the Oligarces paradoxus Meinert.

Says Dr. R. Leuckart, whose article | we have drawn largely
upon in the present account, "This reproduction was said to
commence in autumn, to continue through the winter and
spring, giving origin, during the whole of this period, to a
series of successive generations of larvae, until, finally, in June,
the last of them were developed into perfect and sexually
mature animals. The flies, then, as usual, after copulation,
lay eggs, and thus recommence the developmental cycle just
described."

Professor Leuckart has observed these facts anew in the
larvae of a species of dipterous gall-fly, and which he believes
distinct from the Russian species, found under the bark of a
half dead apple-tree that was attacked by fungi. The young
are developed within the body of the larva-like parent from a

* K. E. Von Bacr, " Report on a New Asexual Mode of Reproduction observed
by Professor Wagner in Kasan." Bull. Acad. St. Petersburg, 1863, pt. vi, p. 239.
Also, Wagner in the Journal of the University of Kasan. 1861.

tOn the Asexual Reproduction of Cecidomyia Larvae. Annals and Magazine
of Natural History, March, 1806. Translated from Zeitschrift f Ur Wissenschaftliche
Zoologie, Bd. xiv.



52 THE CLASS OF INSECTS.

"germ-ball" essentially agreeing with the ovary, and the asex-
ual larvae begin life as egg-like bodies developed from this
germ-ball, just as eggs are developed in the little tubes of
which the ovary is an aggregation. Hence these worms bud
out from the germ-stock, just as we have seen in the case of
the Aphides. Leuckart and Wagner farther agree, that " the
so-called chorion never being formed in either of them, the
vitellus [yelk] remains without that envelope which has so re-
markable and peculiar a development in the true egg of in-
sects." .... "The processes of embryo-formation agree in
all essential points with the ordinary phenomena of devel-
opment in a fecundated egg, exactly as has been proved (by
Huxley) to be the case in the Aphides" .... "The only
difference consists in the germ-chambers of the Cecidomyide
larvae separating from the germ-stock, and moving about freely
in the cavity of the body, whilst in the Aphides they remain
permanently attached, and constitute an apparatus which, in
its form and arrangement, reproduces the conditions of the
female organs."

Thus we can neither pronounce these so-called larvce to be
larvae so long as they produce young, neither are they actual
males or females ; they are what Leuckart calls asexual forms,
which produce false-eggs (pseudova of Huxley, as restricted
by Leuckart). This is paralleled by the asexual Aphides, and
among Hj^menoptera by the worker Ants, and worker, or, as
they were formerly called, neuter Bees, the latter of which have
been known to produce young without the interposition of the
male ; thus the two sexes, at least the females, are dimorphic,
i. e. for certain exigencies of life they are specialized into two
distinct forms, one (as in the asexual Aphis) to produce an un-
limited number of young during the summer ; the other and
sexual, normal form to produce in the autumn a comparatively
limited number of eggs.

Dimorphism is intimately connected with agamic reproduc-
tion. Thus the asexual Aphis, and the perfect female, may be
called dimorphic forms. Or the perfect female may assume
two forms, so much so as to be mistaken for two distinct spe-
cies. Thus Cynips quercus-spongifica occurs in male and female
broods in the spring, while the fall brood of females were



DIMORPHISM. 53

described as a separate species, C. adculata. Mr. B. D. Walsh
considers the two sets of females as dimorphic forms, and he
thinks that 0. adculata lays eggs which produce C. quercus-
tpongifica.

Huber supposes there are two sizes of the three forms (/. e.
male, female, and worker) of Bombus, one set being a little
larger than the other.

Alfred Wallace has discovered that there are two forms of
females of Papilio Memnon of the East Indies ; one is normal,
having its wings tailed and resembles a closely allied species,
Papilio Coon, which is not dimorphous, while the other is tail-
less, resembling its tailless male. Papilio Pammon has three
sorts of females, and is hence " trimorphic." One of its forms
predominates in Sumatra, and a second in Java, while a third,
(described as P. Romulus) abounds in India and Ceylon. P.
Ormenus is trimorphic, as Mr. Wallace obtained in the island
of Waignion, "a third female quite distinct from either of the
others, and in some degree intermediate between the ordinary
male and female." Much the same thing occurs in the North
American P. Turnus. Papilio Glaucus is now known to be a
dimorphic form of the former butterfly, both having, according
to Mr. Uhler, been bred from the same batch of eggs. The
ordinary form of the female of P. Turnus occurs north of lat.
37, while the dimorphic form, P. Glaucus, occurs south of 42.

The male sex also presents dimorphic forms. Mr. Pascoe
(Proceedings of the Entomological Society of London, 1862,
p. 71) states that there are dimorphic forms of Ant h rib idee ;
that they occur in the male of Stenocerus and Micoceros. Six
species of Dytiscus have two female forms, the most common
having the elytra deeply sulcate, while in the rarer forms the
elytra are smooth as in the male.

There is a tendency, we would observe, in the more abnor-
mal of the two sexual forms, to revert to a lower t} T pe. Thus
the agamic Aphis is more generally wingless, and the tailless
female butterfly mimics the members of a lower genus, Pier is.
The final cause of Dimorphism, like that of agamic reproduc-
tion, is the continuance of the species, and is, so far as yet
known, an exceptional occurrence.

Mimetic forms. Many insects often resemble, in a remark-



54 THE CLASS OF INSECTS.

able manner, those of other groups. They are called mimetic
forms. Insects are related to each other by analogy and affin-
ity. Thus the truly tailless species of Papilio, i. e. those where
the tail is absent in both sexes, are related by affinity to Pie-
ris, which has rounded hind wings. They also stand next to
Pier is in the system of Nature. But there are, on the other
hand, mimetic forms, which borrow the features of groups far
above them in the natural system. Thus the Sesia resembles a
Bee, Bombylius and Laphria resemble Bombus; the Syrphus
flies are easily mistaken for Wasps. So in the second series
of suborders of Insects, Forficula resembles the Stapliylinus;
Termes resembles the true Ant ; Psocus, the Aphis; Ascalaphus
resembles Papilio ; Mantispa recalls the Orthopterous Mantis, and
Panorpa reminds us of the Tipulce, (Bittacus being strikingly
analogous to the Dipterous Bittacomorpha) . Thus these lower,
more variable groups of insects strive, as it were, to connect
themselves by certain analogous, mimetic forms, with the more
stable and higher groups.

Comprehensive types are mimetic forms which combine the
characters of other and generally higher groups. Thus each
Neuropterous family contains mimetic forms which ally them
strongly with some one of the six other suborders of insects.
The early fossil insects are remarkable for combining the char-
acters of groups which appear ages after. The most remark-
able comprehensive type is a Carboniferous insect, the Eugereon
Boeckingi mentioned farther on.

HYBRIDITY. Hybrids are sometimes produced between differ-
ent species, but though it is known that different genera unite
sexually, we know of very few authentic instances of the pro-
duction of hybrids therefrom. One is related by Mr. Midford,
who exhibited at the March 4th (1861) meeting of the London
Entomological Society, hybrids produced from a male Pliiga-
lia pilosaria, and a female Nyssia hispidaria. "The males
resemble N. hispidaria, but in color have the lighter and
greener tint and transparency of wing of P. pilosaria."

THE DEVELOPMENT OF INSECTS. Immediately after the fer-
tilization of the egg, the first act in the organization of the



THE DEVELOPMENT OF INSECTS.



55



future embryo is the formation of the germinal layer, or
t(nlt'rni (from the Greek, meaning primitive skin). This layer
is formed at the surface out of a surface-layer of larger, often
nucleolated, cells which nearly encompass the yolk-mass. At
one point there is a break in this cellular layer, and the yolk
granules reach to the surface, so that it appears darker than
the other parts of the egg. This cellular layer is soon resolved
into the blastoderm, or germinal layer, which thickens and
narrows, forming a longitudinal band. This is the first stage
of the embryo, which lies as a thin layer of cells upon the outer
surface of the yolk. Both ends of the body are alike, and we
shall afterwards see that its back lies next to the centre of the
egg, its future ventral side looking outwards. The embryo is
thus bent on itself backwards.

In the next stage the blastoderm divides into a certain num-
ber of segments, or joints, which appear as indentations in the
body of the embryo. The head can now be distinguished from
the posterior end chiefly by its larger size, and both it and the