Manchester Memoirs, Vol. I. (1906), No. 6. 19 



maturation division.' I do not consider the suggestion 

 drawn for a comparison with Arteviia a satisfactory 

 exj^lanation. The parthenogenesis of Arteniia is highly 

 speciaHsed, is the chief mode of reproduction and is 

 probably of old acquisition, whereas both B. mori and L. 

 dispar ox\\y occasionally reproduce parthenogenetically and 

 the nuclear changes in the maturation of their partheno- 

 genetic eggs do not differ essentially from those of the 

 fertile &^^. There does not appear to be any tendency 

 for either a suppression of the second polar nucleus or a 

 fusion of the latter with the &%^ nucleus. 



Petrunkewitsch (76) believes that Brauer's second type 

 of maturation of the parthenogenetic ovum of Ai'teiuia,. 

 where there was a fusion of the second polar nucleus 

 with the egg nucleus, was pathological, as he searched 

 specially for it in material from the same locality and 

 failed to find it. Castle thinks that Petrunkewitsch 

 investigated the winter egg and that the second type of 

 maturation occurs in the summer egg, although Brauer 

 himself does not mention the fact. He cannot, however, 

 bring forward any such reason as this for Henking's and 

 Platner's failure to observe a similar phenomenon in the 

 eggs of B. mori and L. dispar. 



But now there are some more exceptions which 

 Castle's theory would not be able to explain, namely the 

 thelyotokous saw-flies such as Poscilosoma luteohun and 

 others which Doncaster has investigated. In these, the 

 number of the chromosomes of the maturation divisions 

 remains the same and there is no fusion of the nuclei ; 

 the polar nuclei apparently disintegrate. These exceptions 

 to Castle's theory are sufficient, I think, to show that it 

 fails to explain the problem of sex in the parthenogenesis 

 of insects. They are not insignificant in number but form 

 a fair proportion of the cases which have been studied 



