Heredity. 143 



unique potentialities?" he too was forced to fall back 

 upon mysticism. 



(b) Special Pangenetic Theories. Passing from the 

 early hypotheses, we come to a series of theories, which 

 are in varying 1 degrees scientific, and may be fairly 

 enough described by the general designation pangenetic. 

 They have this in common, that they seek to explain the 

 uniqueness of the germ-cell by regarding it as a centre 

 of contributions from different parts of the organism. 



At such different epochs as are suggested by the 

 names of Democritus and Hippocrates, Paracelsus and 

 Maupertuis, incipient theories of pangenesis prophecies 

 of Darwin's were suggested. Thus Democritus main- 

 tained that the "seed" of animals was elaborated by 

 contributions from all parts of the body. Two thou- 

 sand years later, Buffon again regarded the germs as 

 mingled extracts from all parts of the body, or as col- 

 lections of samples from the various organs. If such 

 were indeed the case, Buffon and his predecessors saw 

 no further difficulty, for each contributed sample was 

 supposed to reproduce in the embryo a structure like 

 that from which it originated in the parent. 



In 1864, in his Principles of Biology, Herbert Spencer 

 suggested the existence of "physiological units", de- 

 rived from and capable of development into cells, and 

 supposed that they accumulated in the reproductive ele- 

 ments, which thus became, in some conceivable sense, 

 miniature organisms. 



The best-known theory of this class is, of course, the 

 "provisional hypothesis of pangenesis" suggested by 

 Darwin in his Variation of Animals and Plants under 

 Domestication : 



(1) Every cell of the body, not too highly differenti- 

 ated, throws off characteristic gemmules; 



(2) These multiply by fission, retaining their charac- 

 teristics ; 



(3) They become specially concentrated in the repro- 

 ductive elements; 



(4) In development the gemmules unite with others 

 like themselves, and grow into cells like those from 

 whjch they were originally given off. 



