416 THE CANADIAN NATURALIST. [Vol. ix. 



2nd. The function in its most rudimentary condition must 

 have been serviceable to its possessor, and with each successive 

 upward modification must have been increasingly serviceable in 

 the strugsjle for existence, or the organ that subserves it could 

 not have been improved by natural selection. 



3rd. A series of profitable modifications, if not known at least 

 conceivable, must connect the difl'used and imperfect manifesta- 

 tion of the function in the low ancestral germ with the highly 

 specialized and complex organ that fulfils the function in its 

 most developed form. 



It is not necessary to the present purpose to point out that^ 

 even if in the case of any organ or totality of organs in individuals 

 these three criteria be met, it by no means follows that we must 

 admit genetic connection between the several forms, lowest, 

 higher and highest ; but, undoubtedly, if any one of them fail 

 to be met, the possibility of such connection must be emphati- 

 cally denied. Mr. Darwin says, in the second paragraph of chap. 

 14 of the " Origin of Species " : " If it could be demonstrated 

 that any complex organ existed that could not possibly have been 

 formed by numerous, successive, slight modifications, my theory 

 would absolutely break down." This is true; and it is no less 

 true that we shall have demonstrated an organ that could not 

 possibly have been so formed, if we show one that performs a 

 function wholly unrepresented in its supposed ancestral germ, or 

 a function that until highly developed is quite useless to its pos- 

 sessor, or a function that admits of no complete gradation from 

 lowest to highest. 



He who attempts to account for the origin of functions by 

 heredity, variability, and the survival of the fittest, will not meet 

 his chief difficulties when he considers the great common func- 

 tions of animal life and the organs by which they are accom- 

 plished. The functions of prehension, ingestion, digestion and 

 assimilation of food ; of secretion, of excretion, of sensation, of 

 voluntary motion, of the correlation of sensation to motion ; all 

 these without specialization by separate organs are difi'usely and 

 vao-uely manifested in the lowest amoeboid form. Further, all 

 these functions are not merely advantageous but they are essen- 

 tial to every thing that has animal life, and with each more 

 distinct differentiation of function and specialization of organ 

 they give to the possessor an increased advantage in the struggle 

 for existence. And, again, so numerous are the forms of nature, 



