70 
NATURE 
[May 22, 1873 
ON THE ORIGIN AND METAMORPHOSES OF 
af INSECTS * 
IV. 
ON THE NATURE OF METAMORPHOSES 
13 the preceding articles we have considered the life 
history of insects after they have quitted the egg. It 
is obvious, however, that to treat the subject in a satis- 
(Sapper! 
Fic. 30.—Egg of Phryganea (Mystacides). A!, mandibular segment; C* 
to C5, maxillary, labial, and three thoracic segments; D, abdomen. 
(after Zaddach). 31, Egg of Phryganea somewhat more advanced. 4, 
mandibles ; c, maxillze ; c fs, rudiments of the three pairs of legs 32. 
Egg of Pholcus opilionides (atter Claparede). 33, Embryo of Julus 
after Newport). 
factory manner we must take the development as a whole, 
from the commencement of the changes in the egg, up to 
the maturity of the animal, and not suffer ourselves to be 
confused by the fact that all insects do not leave the egg 
Fic. 34.—Colony of Bougainvillea fruticosa, natural size, attached to the 
underside of a piece ot floating tiinber (after Allman). 36, The medusa 
from the same species. 
in the same stage of embryonal development. For 
although all young insects when they quit the egg are 
termed “ larvz,” whatever their form may be (the case of 
the so-called Pupipara not constituting a true exception), 
still it must be remembered that some of these larve are 
* Continued from p. 31. 
much more advanced than others. It is evident that the 
larva of a fly, as regards its stage of development, cor- 
responds in reality neither with that of a moth nor with 
that of a grasshopper. In fact, insects quit the egg in 
very different stages. The maggots of flies, in which 
the appendages of the head are rudimentary, belong 
to a lower grade than the grubs of bees, &c., which 
have antennz, mandibles, maxilla, labrum, labium, and, 
in fact, all the mouth parts of a perfect insect. The 
caterpillars of Lepidoptera are- generally classed with 
the vermiform larve of Diptera and Hymenoptera, and 
placed in opposition to those of Orthoptera, Hemiptera, 
&c. But, in truth, the possession of thoracic legs places 
them, as well as the similar larve of the Tenthredinide, 
on a decidedly higher level, while in the development of 
the cephalic appendages there is, as already mentioned, 
a marked difference between the maggots of flies and the 
grubs of bees. Thus, then, the period of growth (that in 
which the animal eats and increases in size) occupies 
sometimes one stage in the development, sometimes an- 
Fic. 35.—Portion of Colony of Bougainvillea fruticosa, more magnified. 
other ; sometimes, as for instance in the case of Chloéon, 
it continues through more than one, or, in other words, 
growth is accompanied by development. But, in fact, the 
question is even more complicated than this. It is not 
only that the larvz of insects at their birth offer the most | 
various grades of development, from the grub of a fly to 
the young of a grasshopper or a cricket ; if we were to” 
classify larvee according to their development, we should 
have to deal not with a simple case of gradations only, 
but with a series of gradations, which would be different 
according to the organ which we took as our test. ’ 
Apart, however, from the adaptive changes to which 
special reference was made ina previous article, the differ- 
ences are those of gradation, not of direction. The deve- 
lopment of a grasshopper does not pursue a different 
course from that of a bee or wasp, but the embryo attains 
a higher state before quitting the egg in the former than 
in the latter ; while in most Hymenoptera the body-walls 
and internal organs are formed before the thoracic ap- 
pendages ; in the Orthoptera, on the contrary, the legs 
