GERM CELLS IN NEMATODES, SAGITTA 179 
granular ball (Fig. 53, A, B). This phenomenon was 
reported by Hogue (1910) and such eggs were termed 
“Balleier.”” In these eggs the two cells of the four- 
cell stage which are adjacent to the “Ball” undergo 
the diminution process (Fig. 53, A, AB); the re- 
maining two are stem cells which give rise to the 
germ cells (Fig. 53, A, P). Thus there are two 
“Keimbahnen” proceeding side by side in a single 
egg and four primordial germ cells are produced in- 
stead of two as in normal eggs (see Fig. 51). Miss 
Hogue’s experiments with centrifugal force led her 
to conclude that these must be an ‘“‘unsichtbare 
Polaritét ” or ‘‘ Protoplasmaachse”’ in the egg of the 
Ascaris. Boveri agrees with this and considers 
further that the initiation of the diminution process 
is not determined by the chromatin but by the 
cytoplasm of the egg.! 
2. THe KEIMBAHN IN SAGITTA 
Sagitta has proved to be of considerable impor- 
tance to those interested in the keimbahn of animals. 
Hertwig (1880) figures the four primitive germ cells 
in the gastrula and later stages, proving that these 
cells are early set aside in embryonic development. 
Recently the work of Elpatiewsky (1909, 1910) has 
1 He states that, “Was aber auch hier durch weitere Untersuchungen 
noch erreicht werden mag, Eines halte ich fiir sicher, dass sich alles, was 
iiber die Wertigkeit der primiren Blastomeren bei abnormer Furchung 
ermittelt worden ist, durch die Annahme sehr einfacher Plasmadifferenzen 
erkléren lisst, wogegen die Hypothese einer differenzierenden Wirkung 
des Kerns in jeder Form auf imiiberwindliche Schwierigkeiten stésst ” 
(p. 206). 
