GROWTH AND DIFFERENTIATION OF THE GERM-CELIS 



159 



and even Munson's careful studies do not seem definitely to establish 

 its connection with the attraction-sphere or centrosome of the last 

 oogonium-division. That a body simulating an attraction-sphere and 

 containing a central granule may arise dc novo in the cytoplasm 

 is shown by Lenhossek's observations on the spermatids of the 

 rat (p. 170); and the central granule is in this case certainly not 

 a centrosome, since the true centrosomes are found in another 

 part of the cell. It is quite possible that the "vitelhne body" of 

 Limulus may have a similar origin. Nemec ('97) finds in Polyzoniuin 

 in the earliest stages a single body applied to the nucleus and 

 later two bodies, one of which enlarges to form a cap-shaped yolk- 



Fig. 81. — Forms of yolk-nuclei in Limulus and Polyzonium. \A-C, MUNSON; D-F, Xemec] 

 A. Very young ovarian eggs oi Limu/us ; at the left "vitelline body" (v) in the form of a cap 

 on the nucleus; at the right older egg showing astral formation. B. Older stage of the same; 

 "vitelline body" in the form of an attraction-sphere with central granule. C. Peripheral "yolk- 

 nuclei" (v.».) in Limulus. D. Very early ovarian egg of a myriapod, Polyzonium, with yolk- 

 nucleus. E. Older egg with yolk-nucleus and astral body \a). F. Still later stage, beginning 

 disintegration of the yolk-nucleus. 



nucleus like those described above, while the other assumes the 

 structure of a radiating attraction-sphere containing a central 

 granule (centrosome .''), and his observations suggest that the two 

 bodies in question may have a common origin (Fig. 81). In none 

 of these cases do the astral radiations, surrounding this body, seem 

 to have any connection with cell-division, and it is probable that 

 a careful comparison of their physiological significance here, in 

 leucocytes, and in mitotic division, may give us a better understand- 

 ing of the general significance of astral formations in protoplasm. 



The fate and physiological significance of the yolk-nucleus are 

 still to a considerable extent involved in doubt. In many cases it 



