298 ANNALS NEW YORK ACADEMY OF SCIENCES 



rudimentary and disappears, and we might consider it equally probable 

 that when an organ is much used it would increase in development. The 

 ultra-Darwinians hold that even the loss of an organ is the result of 

 natural selection. The reduction in size of the eyes of moles and their 

 elimination is held to be due to the handicapping of those forms with 

 small eyes through ophthalmia and the greater success in the struggle of 

 the forms with eyes too small to become diseased. This explanation 

 might be satisfactory enough to account for the reduction in size of the 

 eye till it ceased to appear on the surface, but it will not account for the 

 still further steady reduction that goes on after the eye is so rudimentary 

 that it is quite below the skin. In ChrysoMoris, there is a rudimentary 

 but fairly well formed eye far below the surface of the skin. In Noto- 

 ryctes, the reduction has gone to a much further degree, and we find only 

 a trace of the proper eye structure. 



Both Darwinism and Lamarckism, while they can furnish us with plau- 

 sible explanations of increased development, fail to give us any satisfac- 

 tory explanation of the origin of structures. A tooth cusp we could 

 readily believe might be increased by use, but neither Darwinism nor 

 Lamarckism can give us any explanation of why the cusp first appears. 

 It seems probable, too, that there is some other factor which, while ex- 

 plaining the increase in development of a structure, will also account for 

 its origin. 



In the development of mammals, we see many peculiar cases of a paral- 

 lel evolution. The Eocene types, which are ancestral to the later Ungu- 

 lates, have small bunodont teeth, and in a large number of different lines 

 of descent these give rise to cusped teeth of a variety of patterns. Vari- 

 ous explanations of the phenomenon have been given. It would almost 

 appear as if there were in the early types some latent potentiality and that 

 the long cusped teeth are the manifestation of this inherent possibility. 

 Osborn and others have suggested that the evolution has been controlled 

 by this inherent potentiality of the ancestors, but it seems to me that 

 there is nothing in the evolution of the various mammalian groups that 

 cannot be explained as similar modifications to meet similar conditions. 

 The Eocene and Oligocene mammals were probably the first land forms 

 that became adapted to feeding on grass, and it is probably this diet 

 which has resulted in the peculiar development of the Ungulate molars. 



It may be asked if I do not consider that the facts of evolution can be 

 explained by either Darwinism or Lamarckism, to what do I think they 

 are due. I consider that before we can solve this question, we must accu- 

 mulate a great many more facts, and the field is so vast that there is 

 almost endless work and we will be for years accumulating facts without 



