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- 
kérnchen” 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withdrawn, and more recently Amma (1911) has 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 ceruleus (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 A/quorea, 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. 
