170 DR H. P.. FANTHAM 



an unimportant manner — that is, in relation to adaptive 

 structures, wliether past or present — by the direct action 

 of external conditions, and by variations which seem to 

 us in our ignorance to arise spontaneously." This pas- 

 sage also illustrates Darwin's wonderful breadth of view 

 and absence of dogmatism. In it we see that Darwin 

 allowed not only for the Lamarckian methods of modifi- 

 cation, but also for the methods emphasised later in the 

 mutation theory. 



It may be interesting to compare briefly the later views 

 of Darwin and AVallace. Unlike Darwin, Wallace con- 

 served his earlier views entire, and remained a rigid 

 natural selectionist, adopting an uncompromising atti- 

 tude towards Lamarckism. Later, he developed a view 

 that the whole of the organic world had been designed 

 by a First Cause for the ultimate reception of and benefit 

 of mankind. 



Many of the Xeo-Darwinians, unfortunately, followed 

 a view which has proved to be too narrow, in that they 

 made natural selection the exclusive factor in evolution. 

 Chief among these was August Weismann (1834-1914), 

 who, according to Delage, over-emphasised innate charac- 

 ters as against acquired characters, and predetermina- 

 tion as against environmental action. Weismann pro- 

 pounded a hypothesis of heredit}^ based on what he termed 

 the ^^ Continuity of the Germ Plasm." He accepted an 

 older liy})othesis that there were two kinds of protoplasm, 

 namely, a cytoplasm, which can assimilate and grow, 

 and an hereditary substance which he identified with 

 the chromatin of the nucleus. He assumed the continuity 

 of parent and ofl'spring through the germ cells. The 

 germ cells are early separated from the body cells, as 

 can be ascertained by embryological investigations. The 

 germ cells are supposed to retain each a complete sample 

 of the ancestral germ plasm, and so to be directly con- 

 tinuous from generation to generation, thus transmitting 

 hereditary characters. Weismann's hypothesis involves 



