56. THE DOCTRINE OF DESCENT. 
are utterly destitute of air-sacs, and their lungs, like 
ours in early infancy, are not full-grown; a crop is com- 
pletely wanting; gullet and gizzard are, more or less, 
merged in a sac, all conditions very transitory in us, 
and, in most, the nails are awkwardly broad, as with us 
before breaking the shell; the bats, which appear the 
most perfect, are alone able to fly; not the others. And 
these mammals which, so long after birth, are unable to 
find their own food, and never rise from the ground, 
fancy themselves more highly organised than we?’” 
FIG. 7. Fic. & 
Nevertheless, there remains the fact of the parallelism 
of individual development with the systematic series to 
which the individual belongs ; and, among thousands of 
examples, we will select some of the most accessible and 
convincing. Polypes have always been placed systemati- 
cally below the Meduse ; in the development of many 
