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 oi 

 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 ^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 i. 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 



^ 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. 



