NOWLIN : THE VITELLINE BODY IN SPIDER EGGS. 297 



favor the theory that the central clear vesicle is the centrosome, 

 and approaches the nucleus preparatory to the maturation di- 

 visions. But let us follow the body further. We are able to 

 trace it up to the time the nucleus breaks up for the maturation 

 divisions, and, for a period, nothing is plain ; the great massing 

 of yolk has obscured all other structures. It would be most in- 

 teresting to be able to follow the vitelline body through this 

 stage, though I am convinced it takes no part in division. This 

 being a centrolecithal egg, the nucleus and scanty mass of cyto- 

 plasm surrounding it have moved to the periphery of the cell, 

 and there divide, forming a layer of new cells just inside the old 

 cell-wall. The yolk remains undisturbed at the center. The 

 new cells formed by the first few divisions of the mother nu- 

 cleus contain no trace of anything similar to the vitelline body ; 

 that is, the embryonic cells do not possess the structure. But 

 if we look carefully through the central mass of yolk we shall 

 find the vitelline body almost as perfect as before maturation. 

 This indicates that it played no part in the maturation proc- 

 esses, and especially not that of a centrosome. 



Its disappearance varies ; usually it is gone before quite all 

 the yolk globules are absorbed by the growing embryo. 



d. The Vitelline Zone. 



One of the most noticeable feature of many of these follicular 

 eggs is the granular area, called by Balbiani the vitelline zone. 

 In my material I find zones of two kinds. Always there ap- 

 pears the cloud around the nucleus previous to the vitelline 

 body formation. This grows and spreads out considerably into 

 the egg cytoplasm, usually remaining densest around the nu- 

 clear membrane, and gradually blends with the reticulum. The 

 granules composing this zone, as a rule, stain more deeply than 

 the cytoplasm, though I have sometimes found the very oppo- 

 site true. The other zone is perhaps even more marked than 

 this one. It is not found in all eggs, but chiefly in those of the 

 young ovaries. The egg at this time appears to be composed 

 of two parts, an inner sphere, filling about three-fourths of the 

 egg, and an outer lamella. The former is of closely packed 

 granules, with no reticular structure, and stains densely ; the 

 latter is not greatly different, but is much clearer and thinner, 

 with a suspicion of reticulum. There is no gradual blending 



