NUCLEOLI IN PEDICELLINA AMERICANA. 



351 



quent growth and movement toward the center, and finally, in 

 their fusion, the resemblance is quite complete. We may there- 

 fore infer that whatever be the significance of the regularity of 

 the occurrence of these bodies in the males must also hold in the 

 case of the females. 



This striking condition of the nucleoli of the primary germ- 

 cells (Ur-genital Zellen) and of the several generations of sperma- 

 togonia and oogonia can be no mere chance occurrence. In the 

 testes of older individuals, where some of the spermatocytes have 

 already arisen, nearly every resting spermatogonial cell shows 

 the primarily double or the secondarily fused condition of the 

 nucleoli. This period closes, however, with the spermatogonic 

 cycle since the spermatocytic divisions follow without an inter- 

 vening resting stage. In the ovary, where the last oogonial 

 division is followed by a long period of growth, the young 

 oocytes also show the same condition of the nucleoli that has 

 been described for the oogonia. These either persist separately 

 or fuse, but, unlike the nucleoli of the earlier germ-cells, become 

 the composite structures generally found in the nearly matured 

 egg. To this, however, we shall turn below. 



As was pointed out in the discussion of the young polypides, 

 where the internal tissues are not as yet completely differentiated, 



FIG. 4. 



FIG. s. 



the primary germ-cells are not to be distinguished either in size 

 or form from the other embryonic cells. These latter also show 

 the same double nucleoli and act in other respects as do the 

 germ-cells. From this we might expect to find similar condi- 

 tions in the several tissues of the body to which the embryonic 

 cells give rise, and such is, in fact, the case. In polyps, old or 

 young, in males or in females, every organ shows the same con- 



