Chap, iv.] C&CA OF MAMMALS. 171 



associated with a short and wide intestine. With 

 these caeca there must not be confounded the frequently 

 present outgrowth on the small intestine, which is the 

 curiously permanent remnant of the vitelline duct, 

 by which food is obtained from the yolk. 



The caecum of Mammals presents some very re- 

 markable variations ; and we find many exceptions to 

 the generalisation, that it is short in carnivorous and 

 long in herbivorous forms. While its shortness or 

 absence in the true Carnivora would seem to afford a 

 support to the generalisation just indicated, it is more 

 probable that its small size or absence in insectivorous 

 forms, is rather to be associated with the dangers to 

 which the hard chitinous coverings of their food 

 might expose animals that fed on insects ; the same 

 explanation will apply to the insectivorous bats, and 

 one of the same sort to the frugivorous species of 

 Chiroptera, or to the fish-eating otter. At the same 

 time, it is not to be thought that all frugivorous 

 mammals are without caeca ; not only has man a 

 caecum, but the fruit-eating monkeys have one also. 

 Herein we find one of the great arguments against 

 prophesying as to the habits of an animal from what 

 we can see as to its structure, and find a sufficient 

 answer to those who assume that the parts of an 

 animal are in accordance with its habits. The tele- 

 ologist takes no account of that influence which, as we 

 have shown again and again, is no less an important 

 factor than adaptation, the factor of heredity. 



It is clear enough that a cherry-stone impacted in 

 a narrow caecum may produce inflammation, and yet 

 an animal that has been so successful in the struggle 

 for existence as has man, has not only a caecum 

 (which is about two or two and a half inches in. width), 

 but this is continued into an appendix vermiformis, 

 which is not so much as half an inch in width. So 

 far as man is concerned, we may well suppose that he 



