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 completely 

 wanting; a 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 per- 

 fect, 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. 8. 



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 system- 

 atically below the Medusae; in the development of many 



