232 



EEV. J. T. GTJLICK ON DIYEKGENT EVOLUTIOJf 



but if, during its brief period of local divergence, Industrial 

 or Clironal Segregation is introduced, tbe variety becomes 

 more and more dift'erentiated, and, as one after another the 

 different forms of E-eflexive Segregation arise, it passes into a 

 well-defined species. There is, however, reason to believe tbat 

 the order of events is often tbe reverse, Eeflexive forms of 

 Segregation being the cause of the first divergences. 



As Spatial Segregation does not depend upon diversity in the 

 qualities and powers of the organism, so also it does not usually 

 result in distributing the organism in different localities according 

 to their differences of endowment. The causes tbat produce it 

 are primarily separative, not segregative. 



Migration is produced by the natural powers of the organism, 

 acting under the guidance of instincts that usually lead a group 

 of individuals, capable of propagating tbe species, to migrate 

 together ; wbile the organisms that are most dependent on 

 activities in the environment for their distribution, are usually 

 distributed in the form of seeds or germs, aoy one of wbich is 

 capable of developing into a complete community. 



The causes of Separation between the different sections, and 

 of Integration between the members of one section, are therefore 

 sufficiently clear ; but what are the causes of difference of cha- 

 racter in the different sections, especially when they are exposed 

 to the same environment? These causes all come under what I 

 call Intensive Segregation, which, for the sake of saving repetition , 

 will be fully discussed in a separate paper. 



(d) 9. rERTILIZATIOI^AL SeGEEGATION. 



Since writing this chapter on Environal Segregation, I have 

 seen Erancis G-alton's short article on " The Origin of Varieties " 

 published in ' Nature,' vol. xxxiv. p. 395, in which he refers to a 

 cause of segregation that had not occurred to me. He says : — " If 

 insects visited promiscuously the flowers of a variety and those 

 of tbe parent stock, then — supposing the organs of repro- 

 duction and the period of flowering to be alike in both, and 

 tbat hybrids between them could be produced by artificial cross- 

 fertilization — we should expect to find hybrids in abundance 

 whenever members of the variety and those of tbe original stock 

 occupied the same or closely contiguous districts. It is hard to 

 account for our not doing so, except on the supposition that insects 

 feel repugnance to visiting the plants iiiterchangeably." 



