NOWLIN : THE VITELLINE BODY IN SPIDER EGGS. 299 



These epithelial cells no doubt serve as nurse-cells to the fol- 

 licular egg. The wall is not well defined around those oocytes 

 which have just pushed to the surface, and the nurse-cells press 

 into their cytoplasm for some distance. {G, fig. 1.) We find 

 this in still older eggs. Figure IG, plate XIII, shows the epi- 

 thelial cells of the stalk lying in the cytoplasm of the oocyte, 

 entirely surrounded by it in some cases. Whether this is car- 

 ried to a still greater degree and the cells absorbed by the cyto- 

 plasm, as has been suggested by some authors in other material, 

 I cannot say, but figure 27, plate XIV, shows a gradual fading 

 of these cells, which would indicate that some, at least, are 

 being dissolved. As the egg grows toward maturity, and its 

 food supply is about complete, a definite membrane forms be- 

 tween the neck and the contents of the egg. Figure 24, plate 

 XIV, shows the complete formation of such a membrane, and 

 also the reduced size of the stalk. The epithelial cells have, I 

 believe, completed their mission, and the space which they oc- 

 cupy in the ovarian wall is assuming its former appearance. 

 Figure 32 shows the neck about to disappear. 



/. Egg"S without the Vitelline Body. 



Those eggs which do not contain the vitelline body present 

 some differences. The cytoplasm of the young eggs contains 

 much scattered food material. (Fig. 35, pi. XV.) Also the 

 yolk formation begins much earlier than in eggs having the 

 vitelline body. 



VIII. SUMMARY AND INTERPRETATION. 



The vitelline body makes its appearance first in the young 

 oocyte. After the last oogonial division the cell membrane is 

 reconstructed, and for a time the cell grows rapidly. When it 

 has attained a certain size it moves to the periphery of the tube 

 preparatory to forming the follicle. 



The oocyte is occupied for a time in making its way through 

 the ovarian wall. When it is at last upon the exterior, at- 

 tached by a number of nurse-cells to the tube, a small crescent 

 of darkly staining granules can be seen around the nucleus. 

 At a slightly later stage a denser spot in the form of a tiny 

 sphere can be observed in the midst of the granules. 



Let us try to explain the phenomena thus far observed : the 



