312 GENERAL BIOLOGY 



flexible trunk which compensates for the clumsiness 

 of the rest of the body. 



In this survey it is not implied that each of these 

 forms turned one into another, but they do indicate 

 the very probable path of transformation which 

 the elephant has followed in its derivation from the 

 more usual type of mammals. 



FIG. 113. Appendix vermiformis of kangaroo (at left); of human 

 embryo (at right) . (From Jordan and Kellogg, after Wiedersheim.) 



Vestigial Structures. Another sort of evidence 

 for the transformation of species is to be found in 

 the possession, on the part of animals now living, of 

 useless vestiges that correspond with similar func- 

 tional structures possessed by more primitive types 

 which may be assumed to resemble the ancestors 

 of present-day species. The most striking of these 

 structures are the gill -clefts, reminiscent of an aquatic 

 life and characteristic of fishes, but likewise developed 

 in the embryos of reptiles, birds, and mammals, 

 even man himself, although in the higher verte- 



