no r.. DONCASTEK. 



somes, although in each case there are two polar mitoses, is 

 of considerable interest, I know of nothing quite parallel 

 with it hitherto observed in animals, but I think it not 

 unlikely that in the two generations of the Gallflies, one of 

 which is bisexual and the other purely female, a similar state 

 of things may be found to exist. That there may be two 

 types of egg, one of Avhich is reduced and requires fertilisa- 

 tion, and the other not reduced and parthenogenetic, is of 

 course not infrequent, but in such cases the eggs generally 

 have obvious external differences, and the unreduced form 

 has only one polar body. A condition more nearly resem- 

 bling that found in N. ribesii has been observed by Rosen- 

 berg in Hieracium,^ in which the egg-cell in some flowers on 

 a head is reduced and can be fertilised, in others on the same 

 head not reduced and parthenogenetic. But here again the 

 number of maturation divisions is probably not the same in 

 the two cases. In the bee, according to Petriinkewitsch, all 

 the eggs are reduced, but if not fertilised, the somatic 

 number of chromosomes is restored automatically. 



The conclusions here reached may make it necessary to 

 reconsider the provisional hypothesis of sex-segregation 

 sketched in my previous paper, but until further facts are 

 obtained in other species it seems premature to discuss the 

 bearing of my results on the problem of the determination 

 of sex. I have not found it possible, owing to the minute 

 size of the chromosomes, to determine whether aiiything 

 comparable with Wilson's '^leterotropic'' chromosome exists 

 in Nematus. In some figures (e. g. the group represented 

 in tig. 18) only seven chromosomes are visible instead of 

 eight, but when they are so minute it is always possible that 

 two are superposed and not distinguishable apart. 



In conclusion I take this opportunity of expressing my 

 gratitude to Mr. J. E. S. Moore for allowing me to compare 

 some of my preparations with his, and for valuable help in 

 elucidating my sections. 



[Note. — In a series of eggs all laid by one insect on one 



> Brit. Ass., York, 1906. Discussion ou fertilisation, Sects. D and K. 



