GROWTH AND DIFFERENTIATION OF THE GERM-CELLS 155 



subject can best be considered after an account of that bodv. It 

 may be mentioned here, however, that a large number of observers 

 have maintained a giving off of nuclear substance to the cytoplasm, 

 in the form of actual buds from the nucleus (Blochmann, Scharff! 

 Balbiani, etc.) as separate chromatin-rods or portions of the chromatin 

 network (Fol, Blochmann, Van Bambeke, Erlanger, Mertens. Calkins, 

 Nemec, etc.) or as nucleolar substance (Leydig, Balbiani, Will, Lev- 

 dig, Henneguy), but nearly all of these cases demand reexamination. 



— S 



C 



Fig. 79. — Young ovarian eggs of birds and mammals. [Mertens,] 

 A. Egg of young magpie (eight days), surrounded by the follicle and containing germinal 

 vesicle and " attraction-sphere." B. Primordial egg (oogonium) of new-born cat, dividing. C. Kgg 

 of new-born cat containing " attraction-sphere " {s) and centrosome. D. Of young thrusli sur- 

 rounded by follicle and containing besides the nucleus an attraction-sphere and centrosome (s). 

 and a yolk-nucleus (;'.«.). E. Of young chick containing nucleus, attraction-sphere, and f.itty 

 deutoplasm-spheres (black). F. Egg of new-born child, surrounded by follicle ami containmg 

 nucleus and attraction-sphere. 



{c) Yolk-7i?(c!e?(s.—T\\Q term yolk-nucleus or vitelline body ( Dottcr- 

 kern, corps vitcllin) has been applied to various bodies or masses 

 that appear in the cytoplasm of the growing ovarian ^^'^^•^ and it 

 must be said that the word has at present no well-defined mean- 

 ing. As originally described by von Wittich ('45) in the eggs of 

 spiders, and later by Balbiani ('93) in those of certain myriapods. 

 the yolk-nucleus has the form of a single well-defined spheroidal 



