Third. The most typical or most generalized representatives of a 

 group are found also near its centre of distribution, outlying form- 

 being generally more or less aberrant or specialised. 



Many examples from animal and bird lite wore adduced, the most 

 striking being that of the family of hares, which inhabits the whole of 

 the United States. In conclusion the Professor said : 



"While climatic variations are obviously definite, and while t In- 

 direct action of external conditions exerts a powerful influence in 

 moulding at least the superficial characters, these alone go but a little 

 way toward accounting for the profounder modifications that distin- 

 guish the higher groups. Fore\ai{I t poefltbl to conceive 

 that any amount of climatic variations could transform a song spar- 

 row or a robin into a woodpecker or the reverse ; in fact, make a wood- 

 pecker out of any other form of bird. Here functional evolution- 

 change in habits, use or disuse of parts— must come strongly into play. 

 and, to a less degree, food, isolation, interbreeding the struggle for 

 existence, etc. The modification of organs, as the bill, the wings and 

 tail, in birds, is, in my opinion, the result of definite variation, due to 



"The use to which an organ is put and its structure have evidently 

 the relation of cause and effect. Modification of structure follow and 

 are produced by change of habit. * * * As already intimated, 

 my own studies have given no evidence of evolution through fortui- 

 tous variation ; the evidence is all in the other direction. I cannot 

 even conceive of the evolution of a new form through an accidental 

 variation, since the individual in which it appears must iiecessaril y 

 pair with a normal individual, and can thus transmit the new varia- 

 tion only in a lessened degree to its offspring, to be again diluted in the 

 next generation .through precisely similar contingencies, and so on 

 until the original deviation is obliterated." 



Fossil VERTEBRATA.-Professor Cope spoke on the subject from 

 his standpoint. 



He discussed the evidence as to the nature of variation as presented 

 by the extinct vertebrata. He remarked that one difficulty attends 

 this branch of the subject in the circumstance that we do not gener- 

 ally possess enough perfect specimens of any one species of extinct 

 - ' — i been. Thus 

 ; in this case we cannot prove that many variati< 



vertebrate to make sure ot what its variation. 



it is that in this case we cannot prov< - **! b f™ 



character; but it D 



5 that the brauch of the I 



