209 



Another l)elicf aiuono: these workers is that '"pin'e lines" 

 cannot vary, and Johannsen's ex])erinients with heans is nsed 

 as proof. To nio these experiments appear as eontirniation of 

 ^'atnral Selection, for here we have a varying species which, 

 hv selection, can be formed into two or more forms, exactly as 

 reqnired by Darwin's theory. To maintain that if one of these 

 "pnre lines'' were isolated upon an island, where it conld in- 

 crease and spread over a fairly large area, it, wonld never 

 vary is a belief without evidc^nce to support it. Snch a belief 

 recjuires ns to maintain that the few immigrants, which formed 

 the foundations of our insect fauna, were all "impure lines," 

 from which the species, as we now know them, have been 

 sifted out, or that they are all the results of cross-breeding. 



In criticising Darwin's Xatural Selection theory it is 

 sometimes argued that his ''variations" are not inheritable, 

 whereas the A\'hole theory of ]S"atural Selection demands that 

 they should be if they are to take any part in evolution. To 

 divide ''variations" into "mutations" and "fluctuations" and 

 say that Darwin only dealt with the latter is to totally mis- 

 represent Darwin's work. DeVries' "mutations" appear to me 

 to be synonymou? with Darwin's "sports." 



Characters which we may now consider as genetic may 

 originally not have been so. The case of Aiietiiia will illus- 

 trate my meaning: supposing it was to lose the power of liv- 

 ing in fresh water, then the characters it assumed in salt water 

 would be genetic 



"Weismann's theory of the continuity of the germ cells, 

 and his distinction between germ and soma cells, has been 

 used by many writers to support certain theories relating to 

 genetic factors, and the fact is sometimes lost sight of that 

 soma cells are only germ cells modified during the course of 

 ontogeny, and that cell association has an important role in 

 this modification, as polyembryony shows. The capacity of 

 reproducing the whole organism possessed by germ cells is not 

 lost by the soma cells of certain organisms, and is not entirely 

 lost by living cells whilst cell division takes place. 



Causes of Vartatiox. 



The key to evolution lies in the causes of variation, as 

 has been stated by many writers, and of these causes we know 

 next to nothing. That there are manv such causes I have little 



