PORIFERA, CHLENTERATA, VERTEBRATA 73 
Demospongize, and few observations have been 
made upon their archeocytes. These archeocytes 
are of the greatest importance since they give rise 
to the amebocytes and tokocytes (reproductive cells). 
According to Weltner (1907) both amebocytes and 
tokocytes are only physiological states of one and 
the same kind of cell. Many authors have em- 
phasized the importance of the amebocytes, such as 
Gorich (1904), who maintains that this class of cells 
gives rise not only to the gonocytes, statocytes, 
and trophocytes, but also to certain pinacocytes. 
Weltner (1907) goes further than this when he states 
from studies upon the fresh-water sponge that the 
sponge could not exist without amebocytes. 
The earlier investigators almost invariably con- 
sidered the germ cells as mesodermal in origin. 
Lieberkiihn (1856) discovered the eggs in Spongilla 
and later (1859) in Sycandra raphanus. Sponge 
eggs were also observed by Kolliker (1864). Haeckel 
(1872) thought that the eggs were derived from the 
flagellated cells of the gastral epithelium. Schulze 
(1875), on the contrary, maintains that they lie 
deep in the so-called mesoderm; and Fiedler (1888) 
concludes that in Spongilla only certain cells of the 
middle layer may become germ cells. 
Maas (1893) distinguished two sorts of cells in the 
middle layer; one characterized by uniform, fine- 
granuled cytoplasm and an oval nucleus containing 
a very fine net-work of chromatin; the other filled 
with coarse-granuled cytoplasm and a spherical nu- 
cleus containing a deeply staining nucleolus and 
