78 GERM-CELL CYCLE IN ANIMALS 
sparsely over a slide, in the course of a week it will 
be found that the slide is covered with a thin in- 
crusting sponge provided with pores, oscula, canals, 
and flagellated chambers.” Many, at the end of 
two months, had ‘‘developed reproductive bodies 
(eggs or asexual embryos?) ...”? Whether these 
reproductive bodies arose from eggs or masses 
of cells was not determined. “‘ When the plasmodia 
have metamorphosed and the canals and chambers 
have developed, the skeleton makes its appearance.” 
Experiments with Lissodendoryx and Stylotella 
were not quite so successful, but plasmodial masses 
were formed in every case. Further experiments 
proved that “when the dissociated cells of these 
two species [Microciona and Lissodendoryx] are 
intermingled, they do not fuse with one another, 
but fusion goes on between the cells and cell masses 
of one and the same species.”” A similar result was 
obtained by intermingling dissociated cells of Micro- 
ctona and Stylotella. 
Discussion AND SuMMARY. The foregoing ac- 
count of the origin of the germ cells in sponges 
shows conclusively that these cells arise in the so- 
called mesoderm from wandering cells (amebocytes) 
and that amebocytes are descended from archzo- 
cytes which may be distinguished in certain cases 
very early in embryological development (Fig. 27, 4, 
p.g.c). Odgonia and spermatogonia have not been 
recognized by most investigators except in the adult, 
but Maas (1893) has observed them in the planula. 
Jorgensen (1910), who has made the most careful 
