74 GERM-CELL CYCLE IN ANIMALS 



chromatin aggregated into large masses. Only 

 from the latter do the sex cells arise. These two 

 kinds of cells could be distinguished in larval stages 

 and the early separation of germ cells from somatic 

 cells was pointed out. Maas, however, does not 

 insist that there is here a demonstrated continuity 

 of germ cells, since the cells which become sex-cells 

 are separated from the egg by a long series of genera- 

 tions. 



The recent investigations of Jorgensen (1910) 

 on Sycon raphanus and S. setosa have added consider- 

 ably to our knowledge of the origin, structure, and 

 early history of the germ cells of sponges. Jorgensen 

 does not agree with Maas (1893) regarding the early 

 segregation of the germ cells from somatic cells, 

 but finds no particular difference between so-called 

 mesoderm cells and wandering or egg cells. It is 

 worthy of note, however, that the youngest recog- 

 nizable oogonia were found to contain several distinct 

 bodies in their cytoplasm (Fig. 27, 5). 



The method of formation of the gemmules has 

 engaged the attention of many investigators, but 

 several important points concerning it are still in 

 doubt. Gemmule formation is of particular interest 

 since the cells (amebocy tes) , which by most authori- 

 ties are said to give rise to the germ cells, are also 

 considered the cells which form the reproductive 

 portion of the gemmules. At least four views have 

 been held concerning the origin of the gemmule 

 cells : (1) Carter (1849) believed that the gemmule 

 is derived from a single cell, the "ovi-bearing cell"; 



