PARTHENOGENESIS. 2^> 



may play in the economy of the creatures, it is idle to 

 speculate with the scanty knowledge at our command. 

 It is obvious, for one thing, that a greater number of 

 larvas will be produced with complete parthenogenesis 

 than with the mixed, or even with sexual generation ; 

 for every individual that comes to maturity is capable 

 of producing offspring, while with the sexual brood, 

 possibly half of the brood might be males. A con- 

 siderable number of the males born from the par- 

 thenogenetic larvse again may never (and I believe 

 this to be the case) come near the females, and thus 

 are useless, so far as the perpetuation of the species is 

 concerned. Thus it looks as if complete partheno- 

 genesis was more favorable to the continuation of the 

 species than mixed ; and it is clear, from the graduated 

 series of cases we have, from the sexual state through 

 mixed to complete parthenogenesis, as well as from 

 other considerations, that the faculty of dispensing 

 wholly or in part with the males has been acquired. 

 That it is not injurious to the species may be con- 

 cluded ; but I am inclined to believe that, compared 

 with sexual broods, fewer imagos are produced from 

 parthenogenetic larvae ; and if that conclusion is correct 

 (and it is founded on many observations made on Poe- 

 rilosoma pulveratum and Nematus gallicola) it follows 

 that the species are enabled to flourish only through 

 the great number of eggs which are deposited, that is 

 to say, they have less vitality for resisting climatal 

 agencies, or insect or fungoid enemies. My observa- 

 tions, however, are not sufficiently complete to enable me 

 to say definitely that such is the case, but the subject 

 is one well worthy of the attention of entomologists. 



Our present knowledge of parthenogenesis with the 

 saw-flies may be tabulated as follows : 



1. Eggs laid by virgin females yielded males with 

 Nematus ribesii, N. pavidus, N. curtispina, N. miliaris, 

 N. glutinosce, N. palliatus, N. salicis. 



2. Eggs laid by virgin females yielded males and 

 females with Nematus curtispina, Hemichroa rufa. 



