508 



up. The intermediate forms will give us a better idea as to 

 the line of evolution. 



The varieties of such species as Aloha ipomccae, Ilburnia 

 blackbnrni and /. ipontceicola attached to different food plants, 

 require special study, and experiments of change of food and 

 cross breeding should be carried out. 



The cause of the variation of the male genitalia is the 

 fundamental problem of the evolution of these insects. How 

 many genetic characters the aedeagus contains is difficult to 

 estimate. It is also difficult to understand why the genitalia 

 should be the organs chiefly affected by crossings if Lotsy's 

 theory be maintained. 



Weismann and his followers have overemphasized the dif- 

 ference between the germ and somatic cells. There is but one 

 cell and that is the germ cell. The somatic cells being only 

 differentiated germ cells and the differentiation apparently lies 

 wholly within the cytoplasm. Although the chromosomes may 

 be the "bearers of heredity." yet they do not enter into the 

 formation of the "characters." At most they only act upon the 

 cytoplasm. 



If cell division be quantitative (as polyembryony indicates) 

 and not qualitative, how do similar nuclei acting upon similar 

 cytoplasm bring about various differentiations? The nucleus 

 cannot be the sole causation of the differentiation of the cyto- 

 plasm unless we admit a selective and qualitative division of 

 the chromosomes. 



There is experimental evidence to show that the relative 

 position of the cell in the early stages of the embryo influences 

 its development quite irrespective of the nucleus. The influence 

 of certain cells, or their secretions, upon the growth and 

 development of other cells in an organism has been demon- 

 strated by experiments. Among Delphacidae there is a corela- 

 tion between the germ plasm and the external male genitalia, 

 as is indicated by the effect upon the latter brought about by 

 injury to the former by parasites. It is therefore thinkable 

 that an alteration in the germ plasm could bring about an 

 alteration in the male genitalia without any special change in 

 any particular chromosome or chromomere. It is only along 



