STUDIES ON GERM CELLS 457 



nucleus which has in the meantime become smaller (fig. 26, B). 

 These two bodies are considered by Haecker to be identical, and 

 the term 'Metanucleolus' has been applied to them. The meta- 

 nucleolus is, in each division up to the sixty-four cell stage, segre- 

 gated intact in one cell. Its further history was not traced, but 

 in the blastula, when the cells at the posterior pole begin to differen- 

 tiate, nucleolar-like bodies appear in some of them which are 

 absent from the undifferentiated blastula elements (fig. 26, D, n) . 

 These may be the descendants of the metanucleolus. 



A body similar to the metanucleolus was also discovered 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 metanucleo- 

 lus of Aequorea with the spherical body described by Metschnikoff 

 ('86) near the egg nucleus of the Mitrocoma annae, and considered 

 by him as a sperm nucleus. A similar interpretation is given by 

 Haecker for the cytoplasmic inclusion ('Spermakern') found by 

 Boveri ('90) in Tiara. Similarly the 'Kleinkern' which Chun 

 ('91) discovered in the egg cells of the Stephanophyes superba, 

 and the bodies described by Hertwig ('78) near the maturation 

 spindles of Mytilus and Sagitta, resemble very closely the meta- 

 nucleolus of x\equorea. 



Furthermore, the metanucleolus is considered by Haecker 

 homologous to the 'Paracopulationzelle' described by Weismann 

 and Ischikawa in the winter eggs of certain Daphindae (p. 434, 

 fig. 15) and in both cases it is considered probable that these 

 peculiar bodies are restricted to the 'Keimbahnzellen' of the 

 embryo. 



In the eggs of Myzostoma, Wheeler ('97) found that the nucleo- 

 lus of the germinal vesicle does not dissolve soon after it is cast 

 out into the cytoplasm during the formation of the first matura- 

 tion spindle, but remains visible at least until the eight-cell 

 stage, at which time it lies in the large posterior macromere, 

 a cell which ''very probably gives rise to the entoderm of the 

 embryo." Later embryonic stages were not studied. Accord- 

 ing to Wheeler "the nucleoli are relegated to the entoderm cells 

 as the place where they would be least liable to interfere in the 



