GROWTH AND DIFFERENTIATION OF THE GERM- CELLS 



155 



subject can best be considered after an account of that body. 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, Ley- 

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



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. Egg 

 of new-born cat containing " attraction-sphere " (s) and centrosome. Z2. Of young thrush sur- 

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

 and a yolk-nucleus (y.n.). E. Of young chick containing nucleus, attraction-sphere, and fatty 

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

 nucleus and attraction-sphere. 



(c) Yolk-nncleus. The term yolk-nucleus or vitelline body (Dotter- 

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

 that appear in the cytoplasm of the growing ovarian egg ; 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 



