Ebactions and Peodtjcts in- Inteespbcific Ceosses 



103 



This condition was uniformly present in the crosses of the first and second 

 generations in the laboratory, but in the following generations this behavior 

 changed progressively with decreasing percentages present of the female sig- 

 naticollis type, until at the fifth or sixth generation none was present, nor did 

 they appear again in the crossing of the two species as long as the stocks were 

 maintained under like conditions. There is shown ia this series of observations 

 a condition that might be of much importance that would produce unlike results 

 in different locations in nature from the crossing of the two species, permanently 

 altering the history of some individuals. I undertook, therefore, a careful 

 examination of the stocks and attempted to experimentally produce the modifi- 

 cation in behavior that was found. 



Careful examination by measurements, by crossing back upon the fresh stocks 

 from nature and upon older strains that had been longer in the laboratory, failed 

 to show any heterozygous condition present in the gametic constitution of the 

 stock species that could be detected. 



Table 6. 



In nature the average length of ontogeny in L. signaticollis is about 40 days 

 and in L. diversa it is about 60 days. In the records of my cultures I found 

 that the stocks fresh from the natural habitat retained the same rates under the 

 conditions of the quarters at Chicago in the first generation there, but that they 

 progressively changed in this respect, so that at the sixth generation at the 

 latest, often earlier, they had come to have the same rate of development and 

 the same length of ontogenetic period from egg to the adult. In table 6 are 

 given data taken at random from the records showing the rates of development 

 at Cuernavaea, State of Morelos, Mexico, for L. signaticollis Stal, at Orizaba, 

 Vera Cruz, for L. diversa n. sp., and the rates in two stocks at Chicago that 

 were obtained at these locations after the period of probation had passed, when 

 the crossing of the two gave the monohybrid results described. At this time 

 both had the rate of 60 days each, a rate retained indefinitely under laboratory 

 conditions as far as known. 



