‘ : ae ray 
_ the bag, and it is now found to be composed of large cells placed 
side by side. Within it are the globular cells and the cord-like 
_ branching air-tubes. By this time the wings which are visible 
on the 3rd and 4th segments have approached the inside of the 
_— skin of the caterpillar, and when this begins to separate before 
f as cast, a glutinous secretion covers them with the whole 
body. 
The structure of the wings immediately before this period 
recalls that of the membranous expansions with which aquatic 
insects are furnished, with the aid of which they breathe and 
_ move more or less rapidly under water. But the changes on the 
whole of the wing which occur at this time, and during the four 
or five early days of pupal life, soon make these organs compli- 
_ cated. The changes are, however, part of a progressive de- 
velopment. The wing veins, or nervures, without which the 
wings would be flaccid and useless, are formed irrespectively of 
the structures already described. Their path within the wings 
has been marked out by the coil-like air-tubes, but they are 
formed out of the protoplasmic matter which exists amongst the 
layers of globular cells, and are elastic cords surrounded by a 
cellular layer. Whilst they are developing, one or two wide 
air-tubes degenerate, and finally disappear. The veins of the 
wing are attached to the lower surface of the expansion so fre- 
_ quently alluded to, and they grow with the increasing area of 
_ the organs, so that during the early days of the pupa the wing 
consists of an expanded wing membrane, which is cellular, and 
which contains wing veins and large air-tubes, intermingled with 
a great number of globular cells. 
The beautiful microscopic scales of the wing begin to be 
formed as soon as the glutinous case of the pupa is hardened, 
for air soon passes between it and the delicate skin and members 
beneath. By the fifth day all the wings are covered with recog- 
nisable scales and hair, and then for a certain time, depending 
upon temperature and the habit of the species, growth is arrested, 
and things remain 7x statu guo. When the time comes for 
emergence from the pupa case, the imago within awakens, as it 
were, from a long hybernation, and after splitting its case it 
_ comes forth a moist, weakly thing, with its wings crumpled upon 
its sides, wet and unable to move. The sunshine, the dry air, 
and the forcing in of air on the part of the insect into the large 
_ air-tubes of the wing, enable those organs to unfold, to increase 
in area, to decome dry, and at last to be of use. 
It has, I trust, been made evident that the wings are progres- 
sively developed, and that they grow from simple protoplasms 
into all their beauty and complexity of form during the stages 
___ after the escape from the egg. 
__ They are acquired organs ; they are given to the insect during 
its progress of change. Like the metamorphoses, they are 
superadded to the original condition of the embryo or the young 
_ within the egg. They are characteristic, to a great extent, of 
metamorphosis, and thus the notion that the organs and these 
states of change were both. acquired and superadded is worthy 
consideration, 
It now becomes necessay to inquire into the kinds of changes 
which insects submit to during their evolution after birth. There 
are perfect or complete, incomplete and retrograde metamor- 
phoses, and some insects do not change their structures and 
habits at all 
c The cabbage butterfly and the false wasp afford examples of 
___ perfect or complete metamorphosis, the completeness consisting 
_ in the succession of an active larva, an immobile pupa, and an 
_ active imago with different habits to the larva. ‘There is a 
variety of this kind which is of some importance, and it may 
be termed imperfect-complete metamorphosis. The silkworm is 
a good example of this variety, and the organs of its mouth are 
_ imperfectly developed. Such is also the case in many moths 
__ and insects which do not take food of any kind. 
Incomplete metamorphoses are observed in those insects which 
have three stages of activity—active larvae, pupze which move 
and are then called nymphs, and active imagos. 
The common gnat undergoes incomplete metamorphosis, and 
_ the dragon fly, which belongs to a different class, also. The 
gnats skim over the surface of stagnant water and collect their 
eggs together as they are laid one by one in a little boat-shaped 
mass, the whole being covered with a gummy coating. This 
floats, and the larva are hatched very soon from the under side. 
j They commence a life of predacious activity, and undergo skin- 
d sheddings. After one of these the insect comes forth, differing 
in shape from the larve. It swims with the aid of two large 
lamellce, something like a fish-tail, and when it requires air it 
oes 
ATU 
5. 
resents its back on the top of the water, and not its tail, as the 
arva did. This is because there has been an alteration in the 
disposition of the main respiratory tubes. These active pupz, 
or nymphs, cannot eat or drink, and after swimming for some 
days they come permanently to the surface. Then the last 
stage of metamorphosis succeeds, and the tiny gnat escapes 
without wetting its delicate wings, and to pursue a life which is 
well known to you. 
The nymph of the dragon-fly greatly resembles the larva, and 
it seizes prey in the water and devours it. When the time is 
come for the change into the fly the nymph crawls out of its 
element on to a leaf, its skin splits on the back, and the sangui- 
nary and active dragon-fly comes forth. 
In these instances there is not that distinction in habit and 
instinct which prevail amongst the insects gifted with perfect and 
complete metamorphosis. 
Retrograde metamorphosis is a doubtful expression of some 
interesting facts. Sometimes a larva leads an active life, and is 
elaborately and perfectly formed ; it changes into an immobile 
chrysalis, and then the imago comes forth not only with defective 
organs of mastication and motion, but also with indifferent legs 
and scarcely a vestige of wings, Or both wings and legs may be 
wanting, and there is not much resemblance to an insect left. 
Thus the pretty caterpillar, which may still be found about 
geraniums, and which looks like a harlequin from its curious 
tufts of different-coloured hair, belongs to the vapourer moth. 
It is a perfect larva, and very active. The chrysalis, or pupa, 
is, like those of other moths, immobile and swathed. Two 
kinds of moths escape—the males, which are pretty and perfect 
moths, with elegant wings and great powers of fidgetty flight ; 
and the females, which are ugly brown bags with small legs, 
scarcely a vestige of wing, and incomplete mouths. They are 
very unlike the male, and really have not the same activity, 
energy, power of locomotion, or complexity of structure as their 
larva. 
Another species belonging to the genus Psyche has very 
pretty male moths, but the female has no wings, legs, or feelers, 
and looks like a helpless egg-bag. She never quits a curious 
case made up of parts of flowers, in which the caterpillar and 
the pupa lived. 
It is quite clear that in these, insects there is no progressive 
development from first to last in their metamorphosis. 
Insects which do not undergo any metamorphosis are by no 
means uncommon, but they all submit to theskin shedding. Such 
insects are hatched from the egg, in shape and habit much re- 
sembling the adult or full-grown individual, A considerable 
number of the Orthoptera—insects which fold up their wings 
longwise, of which the earwig, the cricket, and the grasshopper 
may be considered as representatives—do not undergo the change 
in form and habit which is so characteristic of most of the In- 
secta. What alterations do occur are the progressive develop- 
ment of wings and of the reproductive organs and skin shedding. 
Most of the Orthoptera moult or change their skins repeatedly, 
some as many as three times, and still they do not alter in form ; 
a fourth skin shedding finds others with rudimentary wings, 
which are small, crumpled, and visible. The fifth moult exhi- 
bits the insects with perfect wings and full-grown. There is no 
period of inactivity, and the insect pursues the same habits 
throughout its lifetime. Its tissues are not subjected to such 
changes as in those described. 
Some few but very important and interesting kinds moult only 
three times, and never have wings; and others, which only 
moult four times, never have these organs in perfection. 
To conclude this short review of the kinds of and exceptions to 
metamorphoses, it must be brought before your recollection that 
the unpleasant louse, the curious fish scale, and the podura, or 
skiptail, do not undergo metamorphoses, and that their skin 
sheddings are not attended by the development of wings. 
Not only are there these varieties of change of structure and 
habits, but there are modifications of each of them which relate 
to the time and season at which metamorphosis takes place, and 
the duration of its stages. 
The next step in the inquiry as to the meaning of all these 
changes in the philosophy of insect life, is to determine whether 
insects which resemble each other have the same kind of meta- 
morphosis—in other words, whether identity of metamorphosis 
accompanies similarity of construction. Are the great groups 
into which the vast class of Insecta is divided by a natural classi- 
fication, capable of being equally well and meaningly classified 
by the similarity or dissimilarity of their particular methods of 
