44 Heredity. 



mother. It is plain that the child of a beardless boy 

 could not inherit the *^ soul-stnff " of a beard in the way 

 Jager imagines;, and this fact alone is enough to show 

 that he has not discovered the true secret of heredity. 



AVe know, too, that reversion, the appearance in the 

 child of the features inherited from a remote ancestor 

 but not shared by its parents, is not at all unusual, and 

 must be regarded as one of the leading characteristics of 

 heredity. It is plain that if the embryonic ovum is, as 

 Jiiger states, unspecialized or '^ de-souled,*' reversion is 

 inexplicable. Accordingly, when he comes to discuss 

 reversion he makes a fundamental change in his hypoth- 

 esis, and holds that when the ovum divides, at a very 

 early stage of its development, into two parts, an onto- 

 genetic portion, which gives rise to tlie new organism, 

 and a phylogenetic portion, which ultimately forms the 

 germinative cells of its reproductive organ, the second 

 part is not unspecialized or '* de-souled" at all, but really 

 retains all the characteristics of the ovum which gives 

 rise to it, and is therefore capable, like the ovum, of 

 giving rise to a new organism. 



As thus remodelled, I believe, and hope to show in 

 the sequel, that Jiiger's hypothesis is a close approxima- 

 tion to the truth, but it is only fair to point out that 

 in its altered form it is not original with Jiiger. The 

 author published almost exactly the same view in 1876 

 ("On a Provisional Hypothesis of Pangenesis," Proc. 

 A))iei\ Assn., 187G, and American Naturalist, March, 

 1877), and it had been stated as long ago as 1849 by 

 Prof. Owen, in his paper on Parthenogenesis, although 

 this author, in his "Anatomy of Vertebrates," after- 

 wards states that he now believes it to be fundamentally 

 erroneous. It is plain, too, that in its second form 

 Jager's In^pothesis is one of evolution, j^ure and simj^le. 



