THE DETERMINATION OF DOMINANCE. 297 



This mating gave larvae in the F^ generation which were of the 

 female parent type, i. e., white without tergal spots in the third 

 stage, and from these emerged a single type of adults, all of the 

 female parental type. These, when inbred, came true, giving 

 individuals like themselves, and continued to breed true for six 

 generations. No traces of sporadic variations of any kind in 

 either adult or larva were found, nor was there in this strain any 

 trace of the male parental type. In this cross, which I have 

 repeated five times, the male type was as completely eliminated 

 as if it had never existed. Plate IV. shows the behavior in the 

 first and second hybrid generations. 



Question as to this result might be raised on the grounds 

 that it is a case of parthenogenesis and not a case of hybrid- 

 ization at all. As a matter of fact, parthenogenesis in Lep- 

 tinotarsa is unknown, and although I have repeatedly endeav- 

 ored to obtain parthenogenetically developed individuals, I 

 have always signally failed. Virgin females of L. undecimlineata 

 have been repeatedly subjected to chemical stimuli (i. e., injected 

 salts of Cu, Na, Li, Sr, Ba, Cu, Zn, etc.), and physical stimuli 

 {i. e., mechanical shocks, electric stimuli, etc.), which might be 

 productive of parthenogenetic development, but thus far without 

 any success whatever. 



In a second series of experiments, an exact duplicate of the 

 first, a female was allowed to develop eggs and deposit them, 

 and these eggs uniformly failed to develop even to the earliest 

 cleavage stages. No development and no fertilized eggs were 

 found from this female until the eggs were fertilized by a male 

 L. signaticollis, when development progressed in the regular man- 

 ner and gave results identical with those of the first experiment. 



L. undecimlineata 9 X d" L. signaticollis. 



Exp. No. H 700 A. 

 A virgin female of L. undecimlineata, from Exp. No. 722, g. 

 Ill (AB), was crossed with a male L. signaticollis, from Exp. No. 

 419, g. XIII (CAAC), under the following conditions: 



Food : Normal — uniform. 

 T. R. H. 



Day Av. 75° F. ±2° . Day Av. 80 per cent. ± 5 per cent. 



Night Av. 70° F. zfc 3.5°. 80-90 per cent. ± 5 per cent. 



