GERM CELLS IN THE ARTHROPODA 163 
ture and significance of these substances will be dis- 
cussed later. 
2. THe KEIMBAHN IN THE CRUSTACEA 
The keimbahn in the Crustacka is best known 
in certain CLapocERA and Coprpopa. Of special 
interest are the investigations of Grobben (1879), 
Weismann and Ischikawa (1889), Haecker (1897), 
Amma (1911), Kiihn (1911, 1913), and Fuchs (1913). 
Grobben (1879) studied the embryology of Moina 
rectirostris and gives a remarkably fine account of 
early cleavage stages, considering the early date 
when the work was done. He figures stages showing 
a foreign body which he considered a polar body, 
segregated in one of the early blastomeres, the segre- 
gation and characteristics of the primordial germ 
cell and the first entoderm cell, and the division and 
later history of the germ cells. His results have been, 
in the main, confirmed by Kiihn (1911, 1913). 
Weismann and Ischikawa (1889) have contributed 
an interesting account of the primary cellular differ- 
entiation in the fertilized winter eggs of six species 
of the Dapunip#, belonging to four genera. The 
germinal vesicle in the eggs of these species casts 
part of its chromatin contents into the cytoplasm 
which there became organized into a “Paranucleus.” 
This paranucleus then acquired a cell body and in 
this condition was termed the ‘‘Copulationszelle” 
because of its future history. In two of the species 
examined this Copulationszelle united with one of 
the first two cleavage cells; in the other four species 
