ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 547 



Artbropoda. 



a. Insecta. 



G-ametogenesis and Sex-determination in Gall-fly.* — L. Doncaster 

 continues his study of Neuroteriu> lenticular is {Spatlwj aster baccarum). 

 He has previously shown (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 

 ten chromosomes in the germ-cells before maturation, while females 

 have twenty, 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 fertilized, giving rise 

 to females of the agamic generation with twenty chromosomes in the 

 ovarian cells. The agamic females appear in early spring ; sexual 

 females and males in early summer. 



Experiment has shown that any individual sexual female has grand- 

 children exclusively or almost exclusively of one sex. The galls produced 

 by sexual females were sleeved, each sleeve containing galls derived 

 from one female parent. In sleeves of galls derived from six females 

 4235 males and 83 females were bred, while in sleeves of galls from 

 another set of six females there were 5139 females and 117 males. 

 About half of the sleeves contained no exceptions, and it is suggested 

 that the exceptions are due to eggs of wild flies laid through the meshes 

 of the sleeves. 



Two possible cytological causes might account for the fact that some 

 sexual females produce only male-producing offspring and others only 

 female-producing offspring. If each fly pairs only once, the difference 

 might depend on the existence of two kinds of males, or it might arise 

 through differences in the maturation-processes of eggs laid by the two 

 classes of sexual female. No cytological difference in the spermato- 

 genesis of different males could be detected. The maturation phenomena 

 of the eggs (about 300) of fifteen separate females were examined, and 

 while they seem to fall into two rather distinct types, the differences are 

 not sufficiently consideral^le to correlate them with the sex-phenomena 

 with any confidence. 



The maturation-processes of the eggs are remarkable, and if, as 

 seems prol)able, the peculiar figures are not due to methods of preserva- 

 tion, they differ widely from the ordinary type of mitosis. The first 

 division takes place by the drawing out of threads (probably double) 

 on each side of the nucleus ; the reticulum becomes absorbed in these 

 threads, which form two groups of parallel chromosomes on a spindle. 

 These chromosomes then divide, probably longitudinally, giving rise 

 to the group which forms the egg-nucleus and three groups of polar 

 chromosomes. 



Spermatogenesis in Belostoma.f — A. M. Chickering has made a 

 preliminary study of spermatogenesis in Belostoma {Zaitha) flnminea, 



* Proc. Rov. Soc, Series B, Ixxxix. (1916) pp. 183-200 (2 pis.). 

 + Trans. Amer. Micr. Soc, xxxv. (1916) pp. 45-56 (.3 pis.). 



