670 
ORIGIN AND TRANSFORMATION OF ANIMALS. 
panying transformation, cause the sexes to approach by 
effacing their more salient characteristics, the respiratory 
activity of the woman comes nearer to that of the man, but 
without reaching so high a limit. 5 ’ 
From transformation we pass naturally to metamorphosis, 
and we find that the larva of an insect or crustacean may be 
regarded as an embryo with an independent life, which obtains 
its own food instead of being nourished by its mother, and 
■which undergoes before our eyes transformations analogous 
to those which the young of viviparous creatures experience 
inside the maternal organism. A proximate cause of meta¬ 
morphosis may be found in the small amount of organizable 
material supplied by the yolk of the eggs of creatures which 
exhibit its peculiar phenomena. In common language, the 
more imperfect the condition in which the egg turns out its 
inhabitant, the more extensive the changes which the creature 
must afterwards undergo. M. Quatrefages observes that, 
compared with the eggs of certain molluscs, those of insects 
are enormous. Thus, the egg of the Cossus ligniperda , is 
about “ thirty thousand times bigger than the egg of a 
teredo. 5 ’ We cannot therefore be surprised that from the 
former there emerges a caterpillar or animal of a complicated 
construction, while the ovum of the teredo yields only a 
simple creature, “ a homogeneous pulp, in ■which a digestive 
tube is vaguely discerned. The first has to fabricate certain 
organs, but its chief work is to develope and modify those 
which it possesses, while the last has everything to acquire. 55 
In contemplating the changes which we can observe in the 
lower vertebrates or molluscs we are insensiblv led to the 
%j 
philosophy of the case. If we observe the gills and tail of 
the tadpole disappear, we must, as M. Quatrefages says, 
exclaim, “Here are organs that become atrophied or dwindle. 55 
If we compare the abdomen of a young crab with that of the 
adult animal, we conceive the idea of “arrested development, 55 
and if we observe the Lernea having its limbs, which first 
acted as oars, changed into a kind of anchor to fasten it to 
its prey, we cannot but admire the way in which nature 
appropriates an existing organ to a novel use, and we find 
the idea of “ transformation. 55 In these and similar transi¬ 
tions there is nothing violent, but all goes on in measured 
order and progression. In our authors words, “the gills of 
the tadpole do not fall off to make room for lungs; the tail 
is not detached, because the legs are ready. Ho ; as the 
one pushes on its growth, with bones, muscles, nerves, and 
vessels, the other diminishes in all its parts. Molecule by 
molecule the one is absorbed; molecule by molecule the 
