78 THB WHENCE AND THE }f HITHER OF MAN 



mode of breathing? There must have been some good 

 reason for this. The most natural explanation would 

 seem to be that he had no projections on his outer sur- 

 face which could develop into gills, and farther, that 

 he could not afford to have any. Now projections on 

 the lower portion of the sides of the body would be an 

 advantage in creeping, but a hindrance in any such 

 mode of swimming as we have described, or indeed in 

 any mode of writhing through the water. 



Furthermore, if he lived, not a creeping Hfe on the 

 bottom, but swimming in the water above, he would 

 have to live almost entirely on microscopic animals and 

 embryos ; and these would be most easily captured by 

 a current of water brought in at the mouth. The 

 whole branchial apparatus in its simplest forms would 

 seem to be an apparatus for sifting out the microscopic 

 particles of food and only later a purely respiratory 

 apparatus. Moreover, we have seen that the parapodia 

 of annelids naturally point to the development of an 

 external skeleton, for their muscles are abeady a part 

 of the external body-wall and attached to the already 

 existing horny cuticle. The logical goal of their de- 

 velopment was the insect. 



Now I do not wish to conceal from you that many 

 good zoologists believe that the vertebrate is descended 

 from annelids ; but for this and other reasons such a 

 descent appears to me very improbable. It would 

 seem far more natural to derive the vertebrate from 

 some free swimming form like the schematic worm, 

 whose largest nerve-cord lay on the dorsal surface be- 

 cause its branches ran to heavy muscles much used in 

 swimming. Later the other nerve-cords degenerated, 

 for such a degeneration of nerve-cords is not at all im- 



