164 CHARLES DARWIN. 



important chapters on bud-variation and anomalous 

 modes of reproduction, and on inheritance. 



The second vokime deals with inheritance, crossing, 

 eflfect of conditions of life, sterility, hybridism, selec- 

 tion by man, causes and laws of variability. Finally, all 

 the main lines are brought to a common centre in 

 the wonderful chapter in which he discloses his " pro- 

 visional hypothesis of pangenesis." This is of such 

 interest, and is so characteristic of its author's power 

 of viewing the most divergent facts from a common 

 standpoint, that it is desirable to give a tolerably full 

 account of it. 



The following is a brief statement of the various 

 classes of facts which Darwin attempted to connect 

 by his hypothesis. 



Reproduction is sexual and asexual, and the latter 

 is of various kinds, although their differences are 

 more apparent than real. It may be concluded that 

 gemmation or budding, fission or division, the repair 

 of injuries, the maintenance of each part, and the 

 growth of the embryo " are all essentially the results 

 of one and the same great power." 



In parthenogenesis the ovum can develop without 

 fertilisation, and hence the union of germs from 

 different individuals cannot serve as an essential 

 characteristic of sexual, as compared with asexual, 

 generation. Although sexually-produced individuals 

 tend to vary far more than those which are produced 

 asexually, this is not always the case, and the vari- 

 ability, when it occurs, is subject to the same laws. 



