1909.] 



Ganietogenesis of the Gail-Fly, etc. 



95 



half the size of the spermatocyte nuclei ; the cells divide completely, and become 

 a pair of spermatids (figs. 16, 17). In late anaphases the small stained body 

 described above outside the nucleus may usually be seen included in one of 

 the daughter cells ; it is found outside the nucleus or spindle during the vf hole 

 process, so cannot be regarded as any kind of accessory chromosome 

 (figs. 12, 13,14, 15). 



It will be seen that the spermatogenesis in Ncurotcrus presents the same 

 remarkable features as have been described by Meves* and Mark and 

 Copelandf in the Bee and Wasp. In each vre find the first spermatocyte 

 division suppressed, being represented by the extrusion of a centrosome with 

 a small quantity of cytoplasm. 



Neuroterus resembles the Wasp in forming two nearly similar spermatids 

 from each spermatocyte, but differs from both Bee and Wasp in having a 

 definite resting stage between the abortive and true divisions. 



The presence of the small stained body, persisting from the primary 

 spermatocyte and passing into half the spermatids, has not been recorded in 

 either Bee or Wasp. 



Development of the Egg in the Ovary. 



In rather young larvae of the summer generation the ovaries consist of 

 masses of cells not yet divided into egg-tubes, but they are beginning to 

 arrange themselves into strands from which the egg-tubes will develop. No 

 clear distinction is yet visible between the cells wliich will become eggs and 

 those which will form the accessory cells between the eggs. The nuclei are 

 mostly large, reticular, with one or two conspicuous nucleoli ; others are stil 

 larger, and have a mass of chromatic material aggregated in the form of dots 

 and fine threads at one side of the nucleus. Nuclei like this may also be found in 

 the eggs in the pupal egg-tubes. Mitotic figures are frequent ; they resemble 

 those found in the body-tissues, and clearly have the diploid number of 

 chromosomes (Plate 1, fig. 19 a, h). 



In young pupae of the summer generation, the stages in the development 

 of the ovarian egg can be followed easily, for the upper ends of the egg -tubes 

 contain very early stages, and at the lower end well developed eggs are found. 

 In the upper ends of the tubes all the cells are alike, but lower down 

 differentiation takes place, and some cellsenlarge greatly, become filled with yolk, 

 and begin to develop into eggs surrounded by follicle-cells. Alternating with 

 the developing eggs are masses of cells with large nuclei, each usually con- 

 .taining a double nucleolus ; these cells are all alike, and do not differ much 



* 'Arch. Mikr. Anat.,' vol. 70, 1907, p. 414 ; vol. 71, 1908, p. 571. 



t 'Proc. Amer. Acad. Arts and Sciences,' vol. 42, 1906, p. 103 ; vol. 43, 1907, p. 7]. 



I 2 



