EVOLUTION OF THE COLORS OF BIRDS. 57 



are we to conceive of these ancestral units, the ahnen- 

 plasmas? Two hypotheses may be given in answer to 

 this question: 



A. Each ahnenplasma unit corresponds to an in- 

 dividual of the species itself; and if put under proper 

 tropic conditions, would, singly, reproduce such an in- 

 dividual. 



B. The ahnenplasmas correspond to the primitive 

 Protozoan ancestors, which, according to theory, could 

 alone reproduce modifications due to external causes 

 (acquired modifications)." 



Prof. Hartog then shows that if hypothesis A be ac- 

 cepted the ahnenplasmas must have varied with the 

 race, but this would make the shufliing process super- 

 fluous as an explanation of variation, and would also be 

 contradictory to thesis II. 



''According to hypothesis B," he continues, " the 

 ahnenplasmas of all Metazoa being similar and Proto- 

 zoan, if the numbers are equal and the shuffling fair, any 

 two parents may beget any offspring whatever; on the 

 plane of thesis V, a lioness might be expected to bring 

 forth a lobster or a starfish or any other animal, which 

 as we know, does noi take place in nature. The only 

 escape from this result is to assume the postulates — (1) 

 that the number of ahnenplasmas varies from species to 

 species; (2) that the number in the combination and 

 not the character of the ahnenj^lasmas determines the 

 species. And as there is not a particle of evidence for 

 the latter postulate, we may say that on hypothesis B, 

 the theory breaks down by its non-conformity with the 

 facts. 



We have then the dilemma, from which I see no 

 escape, that the theory is inconsistent, on A with itself, 

 on B with the facts." 



It is too soon to attempt to pass judgment upon this 



