EVIDENCE FROM EMBRYOLOGY 71 



rodents, occupied by the second and third incisors, 

 the canine and two or more grinders. This conclu- 

 sion is justified by the facts of embryology; for in- 

 stance, in the embryo of the squirrel several of the 

 missing teeth are begun as distinct tooth-germs, but 

 fail to develop, never cut the gum and are resorbed 

 before birth. 



All available evidence points to the conclusion 

 that birds are descended from reptiles, a conclusion 

 which is especially strengthened by the facts of 

 palaeontology and will be examined more at length 

 in the following lecture. Such a descent explains 

 many otherwise puzzling features in the ontogeny 

 of birds, in which reptilian characteristics appear in 

 transitory fashion and are either modified so as to 

 take on typically bird-like character, or are sup- 

 pressed altogether. A remarkable example of this 

 is the formation of rudimentary teeth in certain 

 embryonic birds, followed by their resorption and 

 disappearance before hatching. 



It can hardly be contended that these rudimentary 

 structures, which are confined to the embryonic 

 stages of development and -of which no trace remains 

 in the adult, are so indispensable to the processes 

 of ontogeny, that they were specially created to 

 serve this temporary purpose. For such a conten- 

 tion there is not a particle of evidence and the 

 theory of evolution, which regards these structures 

 as useless remnants, due to inheritance from an- 

 cestors in which the structures were functional, 



