GERM CELLS IN NEMATODES, SAGITTA 18S 



3. The Keimbahn in Other Metazoa 



Certain phenomena have been reported in the 

 early development of the eggs of many other animals 

 which have either been compared or can be compared 

 with conditions such as we have described in the 

 preceding portions of this book. 



The large nucleolus in the germinal vesicle of the 

 medusa, Mquorea forskalea (Fig. 55^ A), according 

 to Haecker (1892), disappears from the germinal 

 vesicle about half an hour after the egg is laid, and 

 a similar body becomes evident near the egg nucleus 

 which has in the meantime become smaller (Fig. 55, 

 B). These two bodies are considered by Haecker 

 to be identical, and the term "Metanucleolus" has 

 been applied to them. The metanucleolus is, in each 

 division up to the sixty-four cell stage, segregated 

 intact in one cell. Its further history was not 

 traced, but in the blastula (Fig. 55, D) when the cells 

 at the posterior pole begin to differentiate, nucleolar- 

 like bodies appear in some of them which are absent 

 from the undifferentiated blastula elements. These 

 may be the descendants of the metanucleolus. 



A body similar to the metanucleolus was also dis- 

 covered by Haecker near the copulating germ nuclei 

 in the egg of Aurelia aurita, but its history could not 

 be determined because of the large amount of yolk 

 present. Haecker identifies the metanucleolus of 

 Mquorea with the spherical body described by Metch- 

 nikoff (1886) near the egg nucleus of Mitrocoma 

 annce, and considered by him as a sperm nucleus. 



