314 N. M. Stevens. 



I. MATERIAL AND METHODS. 



Sections of Aphids from various host plants — the rose, Enghsh 

 ivy, honeysuckle, alder, arrow-head, CEnothera, and hop, were 

 examined; but Aphis rosae proved the most satisfactory for study 

 of the ovogenesis of both parthenogenetic and winter eggs, and 

 Aphis oenotherae for the spermatogenesis. 



Both the Aphids and the winter eggs were killed and fixed with 

 Gilson's aceto-chloroform-sublimate mixture, which gives far 

 better results than any other method tried. Very small Aphids 

 were embedded whole; larger ones after removing the head and 

 thorax. Sections were cut from 5 j" to 7 // thick, and stained with 

 Delafield's haematoxylin and orange G, or with Heidenhain's iron- 

 haematoxylin. The former method of staining gives remarkably 

 good differentiation for ordinary purposes. The latter is more 

 satisfactory for the study of ovogenesis and spermatogenesis. 

 Many slides stained at first with Delafield and orange, w^ere re- 

 stamed with iron-hnematoxylin for more careful study. 



II. PARTHENOGENETIC DEVELOPMENT. 



I. Female Line. 



Most of the stages in ovogenesis of parthenogenetic eggs and also 

 early segmentation stages were obtained from sections of the 

 unborn young of the viviparous female. For more advanced 

 segmentation stages and early embryos very young Aphids were 

 sectioned. 



All the species examined have twelve ovaries in two groups as 

 described by Balbiani (^6()-'j2). Oogonial mitoses were observed, 

 but offered nothing of especial interest as the division figures are 

 identical with other embryonic mitoses. 



The resting oocyte, before the growth stage of the ovum begins, 

 ' has a very large nucleus in proportion to the size of the cell (Figs. 

 I and 2). A large nucleolus occupies the center of the nucleus, 

 and in addition to this the nucleus contains a linin reticulum and 

 irregular masses of material, presumably chromatin, which does 

 not take the haematoxylin stain at this stage. 



One at a time the oocytes at the posterior end of the ovary 

 enlarge and push out into the oviduct, remaining, however, con- 



