The Germ Cells of Aphis. 317 



polar body is given oft. In stud^■ing the development of male^ 

 eggs, one is at a disadvantage so tar as the amount of available 

 material is concerned, because onlv eggs connected with the ova- 

 ries of females which contain embryos large enough to be recog- 

 nized as male can be utilized, while in the female line the best eggs 

 for study are found in abundance in the larger embryos. No 

 polar spindles were found in the few male eggs obtained. Figs. 

 17 and 18 show the polar body as it appears in eggs containing 4 

 and 8 nuclei. There is no indication of fusion of two polar bodies. 

 In Fig. 18 the chromosomes are not so fully fused as in Fig. 17, 

 but this is the condition at a corresponding stage in the female eggs. 

 Examination of the segmentation spindles in male embryos and 

 of spermatogonial mitoses makes it certain that the full somatic 

 number of chromosomes is present until we come to the spermato- 

 cytes when reduction occurs. This is what we should expect had 

 it not been claimed by Castle ('03) that the female character 

 which is usually dominant in parthenogenetic insects is removed 

 from the egg with the second polar body, thus allowing the reces- 

 sive male element to assert itself. There is no evidence in my 

 material of any difference between the maturation of the female 

 parthenogenetic egg and that of the male egg, and until I can 

 procure more material and examine the point further, I shall 

 assume that the method of maturation of all parthenogenetic 

 Aphid eggs is the same, i. e., only one polar body is produced and 

 there is no reduction of chromosomes. There is no mixture ot 

 male and female young in the offspring of one individual: certain 

 apterous females produce only females, either winged or apterous, 

 and others produce only winged males. 



The ovarian oocytes, eggs and polar bodies in the male line 

 (Figs. 16, 17, 18) are noticeably larger than those figured in the 

 female line (Figs. 1-12), but this may be due to the fact that the 

 drawings were made from different species; the former from 

 Aphis oenotherae, the latter from Aphis rosa?. The difference is 

 one of size not of structure, and much the best and most abundant 

 male material was obtained from Aphis oenotherae, where partheno- 

 genetic reproduction was wholly replaced by the sexual method 

 early in October, and young males of all ages were abundant. 



^ 



'Male IS used here merely in the sense that these eggs produce males. 



