130 The Mechanism of Evolution in Leptinotaesa 



'man and others. In this case there is no indication that there is any agent or 

 relation of the juvenile characters in the female stock that are productive of this 

 result, and the conception advanced here seems entirely in harmony with the 

 facts observed. I think no one will deny that the gamete, especially the female, 

 lias at the time of fertilization considerable developmental momentum, as 

 shown by the fact that unfertilized eggs may go on developing for a time without 

 any inciting cause, either fertilization or artificial parthenogenesis, due to the 

 developmental momentum acquired in the growth-period, and that in this period 

 certain directions of reaction and rates of reaction become established and con- 

 tinue on in the zygote, unimpeded by the cross when made under neutral con- 

 ditions, so that this dominance has only a temporary existence and no genetic 

 significance. 



Out of this cross there result 8 pure breeding races that are homozygous in all 

 respects and that continue homozygous without limit either pedigreed cultures 

 or in mass cultures. These appear as shown in table 14, a result different from 

 that present in the cross of signaticoUis X diversa. 



This series shows that in the crossing of species there is no detectable differ- 

 ence in the reaction from that present in crossing intraspecific conditions; in 

 both the reaction is the product of the number of individual agents or the groups 

 of agents that are capable of being dissociated and metathetically redistributed 

 between the gametic systems present. I have made every effort of which I am 

 capable to discover if this instance was not nonconformable to the results of 

 Mendel, or that the interpretation was not correct. There have been abundant 

 complications which will be described presently, but in all the net result has 

 been complete confirmation of the reaction as described by Mendel in his tri- 

 hybrid cross of peas. It may seem a waste to attack this instance so extensively, 

 but the materials have served as the basis of some other investigations, and this 

 served to test fully whether in this respect they were in accord or discord with 

 materials used by other observers. The series has an interesting outcome in the 

 production in F, of 8 arrays that are different in their life-cycle, so that there 

 are 8 potential species which would have been described as species by taxonomists 

 had they been found in nature and their pure breeding and constant characters 

 been determined, and in fact such juvenile differences have lately been made the 

 basis of separation of species of Culicidae by different workers, no doubt with 

 entire correctness, but is it not possible that many of them have arisen or been 

 distributed in the series by processes of this character ? The taxonomist knows 

 nothing of the genetic sequence or constitution in his species, only the fact that 

 the same form occurs repeatedly in the same locations, and genetic continuity 

 is assumed, in most cases with correctness ; but one is made to suspect that the 

 idea has been too liberally applied. 



The reaction that has been described may be called the basic reaction between 

 these two gametic systems, and shows the extent of the dissociation of the sys- 

 tems that takes place under neutral conditions of reaction, and not in any way 

 influenced by external conditions. When, however, differences in the value of 

 the Ac determiner in the medium and in other agents that are present are 

 brought into the complex, then the reactions become much complicated, pro- 

 ducing results that, at first sight, appear entirely at variance with the principles 

 of factorial composition and reaction, and " gloriously non-Mendelian." 



