3i6 N. M. Stevens. 



This is shown in Figs. 14 and 15. Fig. 14 shows an embryo which 

 has just begun to take in jolk (the "secundare Dotter" of Will, 

 '89). At the base oi the embryo as figured are two. conspicuous 

 cells {b^ which apparently guard a valvular opening in the wall 

 of the oviduct, and recall the four guard-cells at the inner end of 

 the embryonic pharynx of Planaria simplicissima. At the lower 

 focus of the section the valve is slightly open and a small amount 

 of yolk material has entered (Fig. 14, a). In Fig. 15 the valve is 

 widely open and yolk cells are being taken into the embryo. 

 Whether the embryo actively sucks in the yolk, or the yolk cells 

 themselves are the active agents, it is impossible to tell, but the 

 former seems more likely. Will ('89) describes the secondary 

 yolk as forming in connection with the follicle epithelium and then 

 being taken into the gastrula. In speaking of the work of Wit- 

 laczil ('84), he says, "Von seiner ganzen Darstellung ist nur das 

 eine richtig, das der secundare Dotter von Follikelepithel seinen 

 Ursprung nimmt," and later he says, "Diese innerhalb der Epi- 

 thelverdickung producirte Dottermasse ist es nun welche in das Ei 

 eintritt und demselben den sogenannten secundaren Dotter liefert. 

 Dass es sich dabei nicht um eine Einwanderung von Zellen . . ." 



The close resemblance in structure between the secondary yolk 

 and certain large cells in the body cavity of the mother was easily 

 observed in the sections, but the relation between the embryo and 

 the vitellaria described above was first seen in connection with the 

 egg of Aleurodes, a related form, where the relation is much more 

 conspicuous than in the Aphid. It was later traced with certaintv 

 in the winter egg and in the parthenogenetic embryo of the Aphid. 



No variation could be detected in the development of ova which 

 produce winged parthenogenetic individuals. The winged 

 young can often be distinguished before birth, and some of the 

 same brood may be winged, others ft>terous. The winged par- 

 thenogenetic individuals are migrants !|nd their appearance seems 

 to be conditioned by the amount or the quality of the food supply. 



2. Male Line. 



The mothers of the males are apterous and cannot be distin- 

 guished externally from the apterous females which produce 

 female offspring. The ovaries show no difference in structure, 

 unless it may be in size and number of the oocytes, and only one 



