594 THE BEGINNINGS OF LIFE. 



in the continuous operation of any internal tendency, 

 whether miraculously or naturally impressed upon living 

 matter, which may lead it to exhibit a tendency to 

 become more and more heterogeneous he, to a cer- 

 tain extent, verges in the direction of those who do 

 believe in the existence of such a tendency. He ad- 

 mits the great importance of the actual constitution of 

 the organism itself, and also the ease v/ith which most 

 important differences in organic form and structure 

 occasionally spring up, by virtue of internal molecular 

 modifications which seem to occur quite indepen- 

 dently of any external causes of change. 



And in spite of all that Mr. Darwin has said con- 

 cerning his belief in the all-important influence of 

 Natural Selection in bringing about specific modifi- 

 cations, we think that many of the very interesting 

 facts which he has recorded in that treasury of bio- 

 logical knowledge, his c Animals and Plants under 

 Domestication,' afford sufficient evidence to prove that 

 Mr. Darwin did not assign sufficient importance to 

 other causes, as producers of specific variation J . We 

 have already alluded to the comparatively low estimate 

 which he attaches to the influence of change in external 

 conditions 2 . We think, moreover, that Mr. Darwin 



1 In this respect, therefore, we agree with Mr. St. George Mivart. 

 (See his ' Genesis of Species,' chap, iv.) 



2 The question whether changes are often initiated in this manner 

 (see pp. 578-582) is, of course, quite independent of the one more 

 recently discussed, which was as to the relative importance of the internal 

 and of the external agencies in the consideration of changes so induced. 



