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. 



FIG. a 



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 Medusae; in the development of many 



