216 GERM-CELL CYCLE IN ANIMALS 



by Herbst (1894, 1895) for the migration of the 

 blastoderm-forming cells from the center to the sur- 

 face of the eggs of certain arthropods. 



Haecker (1897) has suggested that the "Aussen- 

 kornchen" which appear in the egg of Cyclops during 

 the formation of the first cleavage spindle may be 

 nucleolar in nature. Later (1903) this idea was 

 withdrawn, and more recently Amma (1911) has 

 likewise been unable to sustain this hypothesis. The 

 most convincing data furnished by Amma are that in 

 an allied form, Diaptomus cceruleus (Fig. 49, H) , these 

 granules appear before the cleavage spindle is formed 

 and before the nucleoli of the pronuclei have disap- 

 peared. 



The remaining forms in which nucleoli have been 

 considered as keimbahn-determinants are merely 

 suggestive. In JEquorea, Haecker (1892) traced the 

 metanucleolus, which arises from the germinal vesicle, 

 into certain cells of the blastula. Similar bodies 

 appear in Mitrocoma (Metchnikoff, 1886), Tiara 

 (Boveri, 1890), Stephanophyes (Chun, 1891), Myzo- 

 stoma (Wheeler, 1897), and Asterias (Hartmann, 1902), 

 but their ultimate fate has not been determined. 

 Meves (1914), however, has traced the middle piece 

 of the sperm of the sea urchin, Parechinus miliaris, 

 into one of the cells of the animal half of the egg at 

 the thirty-two-cell stage. This middle piece is of a 

 plastochondrial nature. 



It seems probable that in all these cases the same 

 influences may be at work regulating the time, the 

 place, and the method of localization of the nucleoli. 



