ij2 Relationship of the Parthenogenetic to 



As a rule the males of this species appear first and 

 may be easily distinguished from the females ; it is 

 therefore easy to separate the sexes, and so prevent 

 fecundation. If the unfertilized females are put with 

 the lepidopterous pupae, they usually proceed to pierce 

 them at once. I have frequently tried this experiment, 

 usually with the result that the unfertilized females 

 only produce males. The result of one experiment 

 was as follows. 



In the spring of 1876, I collected a quantity of Pieris 

 brassicae pupae which had been pierced by Pteromaliis 

 piiparum. At the same time I had reared caterpillars 

 of Vanessa urticae which pupated in June. These 

 pupae were pierced by the unfertilized female Pteromali. 

 To be quite sure, I examined the receptaculitm seminis 

 and w^as perfectly certain that fecundation had not 

 taken place. These pierced pupae gave the following 

 results. 



ist Pupam24c?. 3rd Pupa=:75c?5P. 



2nd Pupa= 62(^. 4th Pupa =45 (^4 p. 



I will add an instance from the rose-gall Cynipidae, 

 showing that parthenogenesis is developed directly 

 from the sexual generation. I have experimented with 

 both Rhodites rosae and Rhodites eglanteriae. I have 

 reared hundreds of the former species, and have 

 received the results of other observers, and they all 

 show that the males occur in a very small proportion, 

 about 2 7o only. Owing to the rarity of the males, most 

 of the females are unfertilized, a fact which is confirmed 

 by experiment, for all the flies soon after leaving the 



