88 GERM-CELL CYCLE IN ANIMALS 
engulfing other primitive ova. Only six or eight, 
rarely more, of the eggs survive. 
In Clava, according to van Beneden (1874), the 
ova arise in the entoderm. Weismann (1883) was 
not able to determine whether they originated in 
the entoderm or migrated into that layer from the 
ectoderm, but he was certain that the male germ cells 
were ectodermal. This conclusion regarding the 
male germ cells was confirmed by Thallowitz (1885). 
Harm (1902) was able to trace the primitive germ 
cells back to a very early stage, and could distinguish 
them in even young hydranths. The odcytes dif- 
fered from the remaining ectoderm cells in the pos- 
session of a larger amount of cytoplasm, a larger 
nucleus with a big nucleolus, and an ameboid shape. 
Hargitt (1906), working on Clava leptostyla, comes 
to conclusions different from those of Harm on C. 
squamata. He says “that eggs probably never arise 
in the ectoderm but always in the entoderm of the 
peduncle of the gonophore, or in that of the polyp very 
near the base of the gonophore. ... Clava, like 
other Hydroids, has its breeding season, during which 
the germ cells are extremely abundant, and at other 
times these cells are either entirely absent or very 
scarce” (p. 208). Concerning the early origin 
of germ cells Hargitt says, “it may not be im- 
possible that ‘Urkeimzellen’ should perhaps exist in 
undifferentiated stages, still the probability is so 
extremely remote as to render doubtful to a degree 
any but the most thoroughly substantial claims ” 
(p. 209). 
