208 



Orthogenesis. The fact that parallel development, such 

 as the reduction of the two frontal carinae to one, has taken 

 place not only within the Alohini but also within other sec- 

 tions of the Delphacidae, w^ould lead one to suppose that there 

 is a fundamental law acting in each group. Even if it could 

 be shown that this reduction w^as of a utilitarian nature, and 

 thus open to the influence of Xatural Selection, it would sug- 

 gest that a common cause brought about the variation in each 

 group. 



Lama)-cl-icw factors. Of true Lamarckian factors I can 

 see no evidence among the material under discussion, unless 

 short wings originated through disuse. I have also suggested 

 that the develoj^ment of the elongated head in Dictyopkorodel- 

 phax may be due to mechanical causes. 



Mendelisni. Mendel's law states the manner in which 

 characters are inherited in balanced crosses, and explains why 

 certain cbaracters are not "swamped" by crossing. Around 

 this law^ there has growii up certain theories of genetic fac- 

 tors. According to certain Mendelian workers all variation 

 is due to the loss of one or more inhibiting factors. This is 

 a belief which I cannot prevent anyone from holding who 

 wishes to do so, but I hope such believers will not try to pre- 

 vent me from disbelieving it. When I think of the primeval 

 cell containing all the genetic factors and inhibitors of all past, 

 present and future specific characters my credulity breaks 

 down. Even when I consider the invisible complexity of the 

 aedeagus of the original ancestor of the Aloha group, as neces- 

 sitated by this theory, my imagination fails me. If evolu- 

 tion were progressive only, then the theory of inhibiting fac- 

 tors would be simplified, but degeneration is as much a part 

 of evolution as progression. The idea that the loss of in- 

 hibiting factors could bring about complexity and then, con- 

 tinued still further, bring about degeneration, appears to me 

 very improbable. One would have to postulate double and 

 triple sets of inhibiting factors. 



If w^e consider the case of the transformation of two frontal 

 carinae into one w^e must believe that the inliibiting factor is 

 lost at the last ecdysis, for up to that period there exists two 

 carinae. In other cases where ontogeny follows the same 

 course as phylogeny we must suppose the inhibiting factors to 

 be present in the germ and to be lost during development. 



