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- 

 ciona 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 archaeo- 

 cytes which may be distinguished in certain cases 

 very early in embryological development (Fig. 27, A, 

 p.g.c). Oogonia 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 



