The Germ Cells of Aphis. 315 



nected by a stalk with the central core of the ovary (Fig. i). As 

 many as three eggs may be thus connected by stalks with the cen- 

 ter of an ovary, — one egg just passing into the oviduct, another in 

 maturation stage, and a third in 8 to i6-cell stage. As the oocyte 

 increases in size, the cytoplasm changes its staining reaction, 

 coloring somewhat deeply with Delafield; and the nucleus shows 

 various changes. The nucleolus disappears and the chromosomes 

 become stainable at an early stage (Figs, i, 3, 4, 5). As the egg 

 rapidly enlarges the nucleus approaches the periphery at one side 

 of the oval egg (Fig. 6). Just before maturation, clear vesicles 

 appear in the cytoplasm and soon fuse forming large irregular 

 spaces filled with a clear non-staining substance, presumably yolk 

 material, separated from the general cytoplasm (Blochmann). 



Fig. 7 shows the equatorial plate of a polar spindle in metaphase. 

 There are 10 chromosomes of 5 different sizes. This is the so- 

 matic number, and there is therefore no synapsis or conjugation of 

 chromosomes and no reduction in the maturation of the female 

 parthenogenetic egg. The same number (10) and the same varia- 

 tion in size (5 pairs) is shown in the segmentation spindles and 

 equatorial plate of Fig. 12. The maturation spindle in anaphase 

 is well shown in Fig. 8; also the lacunar spaces in the interior of 

 the egg. 



The polar body is at first completely extruded from the egg and 

 separated from it as seen in Figs. 8 and 9. It is distinctly a polar 

 body not a "polar nucleus." Soon, however, it comes to lie 

 within the boundary of the egg among the segmentation nuclei 

 (Figs. 10 and 11). In such a stage as in Fig. 11, the polar 

 body is easily recognizable by its clear cytoplasm and deeply- 

 staining mass of chromatin. It lies in a sort of vacuole in 

 the egg-cytoplasm. I have been able to follow the polar body 

 as far as the stage shown in Fig. 13. The cytoplasm can 

 no longer be distinguished from that of the egg; the chromatin 

 mass is irregular in outline, usually stains less deeply and appears 

 to be degenerating. I therefore feel sure that the polar body takes 

 no part in the development of the embryo. Its inclusion within 

 the egg is probably due merely to mechanical conditions, /. ^., to 

 the pressure of the walls of the oviduct upon it, as it lies on the 

 side of the oval egg. 



There is only one point of especial interest in the later develop- 

 ment, and that is the relation of the young embryo to the vitellaria. 



