xi \ Erste Sektion: Cytologie und Protozoenkunde. Erste Sitzung. 



nucleus or cytoplasm. Other students of protoplasm have made 

 similar observations. 



But it is maintained by some — on what grounds is not quite 

 clear — that this extruded substance assumes the character of archo- 

 plasm which in turn is responsible for the appearance ,,de novo" 

 of an attraction sphere, centrosome and aster. 



According to this view, the centrosome and aster are tempo- 

 rary arrangements of the protoplasmic granules; or, in case of an 

 alveolar protoplasmic structure, merely temporary, linear arrange- 

 ments of the vesicles during caryokinesis ; the centrosome and 

 aster being considered temporary dynamic arrangements which 

 disappear when the dynamic forces are again at rest. 



That this is an erroneous interpretation will appear, if it can 

 be shown that the aster and centrosome may exist independently 

 of this extruded substance, and that the socalled Nebenkern, or 

 Yolk-nucleus, are indeed different. That the latter is the case, 

 can be seen from an inspection of figs. 6—12, pl. Ic, representing 

 sections of the ovarian egg of Clemmys. 



The centrosome and aster in these eggs can be tra- 

 ced back to the aster and centrosome in the dividing oogonia; and 

 are clearly not new formations from the extruded nuclear chro- 

 matin as some observers have maintained of other eggs. 



The centrosome and aster form, what (for want of a better 

 term) I have to call a „receptacle" into which the extruded sub- 

 stance (metaplasm) most readily flows; and consequently it often 

 happens that the metaplasm entirely obscures the aster. Fig. 6 

 represents a section of a very young egg, showing the centrosome 

 and aster as a crescent-shaped archoplasm, partly surrounding 

 the germinal vesicle. In fig. 7, the astral rays are spread out; 

 and the meshes between are filled with the granulär metaplasm. 

 In many cases, this conceals the rays; and, in most cases, also 

 the centrosome. I take the clear, round body, in the center of 

 the large cytocenter (fig. 7) to be the centrosome, which appears 

 more clearly in fig. 6. I do not see how such a thing could be a 

 mere accident. My interpretation is sustained by the appearances 

 in fig. 8. It is here seen, that the extruded metaplasm has pushed 

 the centrosome and aster farther away from the germinal vessicle, 

 and has accumulated between them instead of flowing all around 

 them. That this metaplasm does change its position in the egg; 

 that it actually flows is evident from its final distribution throug- 

 out the cytoplasm. It appears first in surprisingly large quantities 

 in the immediate neighbourhood of the germinal vesicle, gradually 

 accumulating in that area which is occupied by the centrosome 

 and aster; and then spreading out radially, as if flowing between 

 the meshes of the astral rays. In fig. 9 can be seen the intimate 

 connection of this yolk-nucleus, or metaplasm, with the germinal 



