POPULAR SCIENCE REVIEW. 
374 
German physiologists. The author, in passing, pays a just tribute to 
the celebrated Schwann, whose theories, at one time almost universally 
accepted, have long since been found to he formed upon false premisses 
and imperfect observations. But, as he observes, like all general doctrines 
which bind together a great number of isolated facts, this cellular theory 
has at once cleared and widened the field of research. Transformation, 
however, in the form of growth, continues to take place in the higher 
animals after exclusion, but it is worthy of remark, that it is often of a 
kind which Milne Edwards designates as recurrent development, as in the 
case of the higher monkeys, which at birth not a little resemble man, 
hut, from a certain moment, their development, instead of raising them, 
lowers them in the animal scale, making more and more wide the breach 
between them and the human species. 
The metamorphoses of animals in their restricted sense are of course best 
illustrated by those which are exhibited in the class of insects, in which 
there is apparently a sudden change from the grub to the chrysalis ; and 
from the chrysalis to the imago or perfect insect. But these changes are 
really very gradual, and the aphorism “ Natura nihil fit per saltum,” is 
fully borne out in their case. We have not space to follow our author 
through the interesting and lucid details which he gives concerning the 
metamorphoses of insects in general, of myriapods, Crustacea, annelids, mol- 
luscs, reptiles, and batrachians, all of which exhibit features of striking 
and peculiar interest. Instead, however, of regarding the various forms 
presented by an insect, for example, in each of its metamorphoses, as dis- 
tinct beings, of which the first inclosed and nourished the second, (as 
Reaumur would have done,) by the light of modern science we are en- 
abled to perceive that they are but the same being in stages analogous to 
those presented to our notice by the embryo, the foetus, and the young 
of mammiferous animals. And the very proof which Reaumur invoked 
in favour of his view, viz., the dissections of Swammerdam, who could dis- 
tinguish in the advanced caterpillar the antennae, wings, &c., of the perfect 
insect, shows the gradual and progressive nature of the change to which 
they are subject. The caterpillar for us is an embryo which, in order to 
become adult, has not only to grow, and to develop itself as an infant 
would, but also has to pass through certain changes analogous to the 
embryonic changes of higher animals. The rapidity of growth, too, which 
is so remarkable a character in the primary conditions of insects, is one 
which is eminently analogous to the embryonic condition ; and thus a 
larva may be considered as an independently existing embryo, which 
nourishes itself, instead of being fed by its mother, and undergoes extern- 
ally, before our eyes, changes or transformations analogous to those which, 
in the case of viviparous animals, are accomplished within the maternal 
organism. 
The phenomena of the third kind, which are placed under the collective 
title of geneagenesis, dovetail, as it were, into the other two, as facts of 
progressive growth and individualization. Here we find animals which, 
rigorously speaking, appear to have neither father nor mother, but only a 
parent, which forms them at the expense of its own substance. We find, 
as it were, sons which never resemble their father, and which produce 
