Gametogenesis and Sex-Determination in the Gall-Fly. 183 



is suggested that the cell membrane or cytoplasm is constituted by a hetero- 

 geneous system of lipoids, proteins, etc., held together in a magma containing 

 a gel-forming substance with physical properties similar to those of the 

 cholates. On such a hypothesis, the biological action of certain substances 

 can be explained in a manner more satisfactory than is possible by the 

 assumption of the " lipoid " theory of Hans Meyer and Overton. 



Gametogenesis and Sex-Determination in the Gail-Fly, Neuroterus 

 lenticularis (Spathegaster baccarum). — Part III. 

 By L. Doncastbr, Sc.D., F.E.S., Fellow of King's College, Cambridge. 



(Received January 13, 1916.) 



[Plates 6 and 7.] 



In two previous papers on the maturation of the eggs and spermatozoa 

 and determination of sex in Neuroterus lenticularis* 1 showed (1) that any 

 individual female of the agamic generation produces either male or female 

 offspring, but not both ; (2) that the eggs of some agamic females undergo 

 a reduction division at maturation, while those of others do not ; (3) that, 

 since males have 10 chromosomes in the germ-cells before maturation, while 

 females have 20, the eggs which undergo reduction produce males, and those 

 which do not, produce females ; (4) all eggs of the sexual generation 

 undergo a double maturation division, and are fertilised, giving rise to 

 females of the agamic generation with 20 chromosomes in the ovarian cells. 

 The maturation divisions in the eggs of the sexual generation were described 

 as of a rather peculiar type, and some difficulty was experienced in forming 

 a clear and connected idea of the process. 



One important problem remained unsolved — the nature of the difference 

 between the male-producing and female-producing females of the agamic 

 generation. No difference was discernible between the flies of the two types, 

 nor could any difference be found between their chromosome-groups in the 

 ovarian divisions. A tentative suggestion was made that the difference 

 might depend on the existence of two kinds of spermatozoa, one of which 

 might cause the fertilised egg to develop into a male-producing, the other 

 into a female-producing agamic female, and this suggestion seemed to gain 



* 'Eoy. Soc. Proc.,' B, vol. 82, p. 88 (1910) ; and B, vol. 83, p. 476 (1911). 



