GROWTH AND DIFFERENTIATION OF THE GERM-CELLS 



159 



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

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

 oogonium-division. That a body simulating an attraction-sj)here and 

 containing a central granule may arise dc ?iovo 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 centrosomcs are found in another 

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

 Liviiihis may have a similar origin. Nemec ('97) finds in Polyzoniuvi 

 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- 



D 



Fig. 81. — Forms of yolk-nuclei in Limidus and Polyzonium. [./-C, MrNSON; D-F, Np:mkc.] 

 A. Very young ovarian eggs oi Llmulus ; at the left "vitelline body" (t-) 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" {y.n.) in Liviulus. D. Very early ovarian egg of a myriapod. Polyzonium, with yolk- 

 nucleus. E. O der egg with yolk-nucleus and astral body ^a). F. Still later stage, beginning 

 disintegration of the yolk-nucleus. 



nucleus Hke 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 under*^tand- 

 ing of the general significance of astral formations in protoplasm. 



The fate and physiological significance of the yolk-nucleus arc 

 still to a considerable extent involved in doubt. In many cases i1 



