NOWLIN : THE VITELLINE BODY IN SPIDER EGGS. 301 



some function unencumbered ; but it is a complete giving way, 

 central vesicle and all. 



The yolk, pressing more and more to the center, drives the 

 nucleus and vitelline body inward, until we find them again 

 close together, connected by the scanty remnant of cytoplasm 

 which persists. Of course, this could take place only in those 

 eggs where the vitelline body does not disintegrate, and, as a 

 rule, the structure persists very long after this stage. 



Just before maturation the nucleus moves to the periphery of 

 the cell, leaving the vitelline body at the center. Here the 

 nucleus divides, unaided in any way by tlie structure, which 

 Munson believes to be the "centrosome of the growing oocyte," 

 and, lying undisturbed at the center of the cell, can be seen the 

 vitelline body, even after numerous layers of cells have been 

 formed. Balbiani found the body distinct in embryos two 

 weeks old. The body fades when the yolk is about to be ex- 

 hausted, or, we might say, is finally absorbed along with the 

 yolk by the cells of the developing embryo. 



This convinces me that the vitelline body contains no centro- 

 some, but is merely a condensation of certain food-substances, 

 which the protoplasm of the cells of certain spiders cannot im- 

 mediately break down and use. Its absence in some families 

 is due to those cells possessing engemes sufficient to dissolve 

 these substances more rapidly. 



More than this, structures identical with the central vesicle 

 of the vitelline body have been found in eggs which at the 

 same time possess perfectly distinct vitelline bodies. (Fig. 21, 

 pi. XIV, and fig. 27.) 



BIBLIOGRAPHY. 



( 1 ). Balbiani, E. G., 1893. Centrosome et Dotterkern : Journ. de 

 r anat. et de la physiol,, XXIX. 



(2). Calkins, G. N,, 1895. Observations on the Yolk-nucleus in 

 the Eggs of Lumhrwus : Trans. N. Y. Acad. Sci., June, 1895. 



(3). Crampton, H. E., 1899. The Ovarian History of the Egg of 

 ■Molgula: J. M., XV, Suppl. 



(4). Foot, K., 1896. Yolk-nucleus and Polar Rings: Ibid., J. M., 

 XII, I. 



(5). Henneguy, L. F., 1893. Le Corps vitellin de Balbiani dans 

 ra3uf des Vertebres : Jour, de 1' anat. et de la physiol., XXIX. 



