278 Heredity. 



that produce new organisms, but rather the cells themselves, or 

 units constituting the whole body. 1 



It may be observed that no valid objection can be drawn from 

 the extreme minuteness of these gemmules, our notions of size 

 being purely relative. When we bear in mind that the ascaris 

 may produce about 64,000,000 ova, and a single orchid nearly 

 as many million seeds; and that the organic particles emitted 

 by scent-secreting animals, and the contagious molecules of certain 

 diseases, must be of excessive tenuity, the objection will not 

 appear very weighty. 



Hence, ' we must consider each living being as a microcosm, 

 made up of a multitude of organisms capable of self-jeproduc- 

 tion, of inconceivable minuteness, and as numerous as the stars 

 of heaven.' This hypothesis enables Darwin to explain a great 

 number of phenomena, very different in appearance, which, how- 

 ever, physiology regards as essentially identical. Among these 

 we may name gemmiparity, or reproduction from buds, fissiparity, 

 where reproduction is effected by spontaneous or artificial division, 

 sexual generation, parthenogenesis, alternate generation, the de- 

 velopment of the embryo, repair of the tissues, growth of new 

 members in place of those which are lost (as occurs in the case 

 of the lobster, the salamander and the snail) in short, all modes 

 of reproduction whatsoever, and all the modes and all the varieties 

 of heredity. 



We have seen that a distinction may be drawn between characters 

 which are developed and those which are simply transmitted. 

 Transmission may take place without development, as is proved 

 by the very numerous facts of atavism and reversional heredity, 

 whether under the direct or the collateral form. This phenome- 

 non, which we have compared with alternate generations, is very 

 well explained by Darwin's hypothesis. The common fact of a 

 grandfather transmitting to his grandson, by his daughter, cha- 

 racters which she does not or cannot possess, can only be under- 

 stood on the supposition that in the daughter they exist in the 

 latent state; or, to give a physiological basis to this idea, gemmules 



1 Darwin, Variation, etc., vol. ii. chap. xvii. 



