>66 



HARDWICKE'S SCIENCE-GOSSIP. 



on the sexual elements at all." Hence Mr. Galton 

 only adopts the theory of Pangenesis as sitppkmcntary 

 and subordinate, to explain the cases in which ac- 

 quired characters may possibly be transmitted ; he 

 explains the primary facts of heredity by his theory 

 of the continuity of the reproductive elements. By 

 adopting this position he dispenses with Darwin's 

 conception of gemmules representing every stage in 

 ontogeny, and thus although he believes the *'or- 



Professor Nageli's theory of heredity (with which 

 1 am only acquainted through Professor Weismann's 

 criiicism) is intimately bound up with his ideas of 

 phylogeny or race-development, with which we are 

 not concerned, but of that portion which deals v/ith 

 the two problems which we are keeping before us, a 

 short account must be given. 



Professor Nageli's hypothesis reminds us to some 

 extent of Pangenesis, and to some extent of Mr. 



ganic units " of adult structure to be preformed in the 

 germ, we can conceive of the separate "representa- 

 tive" gemmules developing epigenetically into the 

 adult structure. This does away with the difficulty 

 expressed by Professor Weismann in the criticism 

 above quoted. Mr. Galton's theory approaches 

 Professor Weismann's, but is nevertheless distinct 

 from the latter. We shall discuss the points of 

 difference more fully hereafter, and reserve' our 

 criticisms till then. 



Spencer's hypothesis, but to its author belongs the 

 credit of originating the valuable conception of 

 "idioplasm." Professor Nageli supposes that there 

 is a network of solid substance extending throughout 

 the body, which determines the specific character of 

 the organism. This is idioplasm, and although 

 differing qualitatively in different species, its nature 

 is fundamentally the same in the different parts of the 

 body of the same organism. The development of an 

 organism is dependent upon the successive activity of 



