GERM CELLS IN PEDICELLINA AMERICANA 9 



Under such conditions it is rather difficult to determine the 

 proper sequence of the divisions ; yet this difficulty can be, in 

 a great measure, overcome by examining the different degrees 

 of development within the different polypides. Thus, where 

 there is no line or series of progressive development within the 

 testis itself, an artificial series can be constructed from the 

 youngest to the oldest testes. Accordingly, I shall first 

 describe the condition to be found in a very young polyp — one 

 shortly after the period of metamorphosis. Here, lying in 

 their proper place, are the primary sperm cells from which all 

 the later generations will arise. These cells are nearly all in 

 the resting stage, and have not as yet sufficiently increased in 

 numbers to fill up the space inclosed by the germinal epithe- 

 lium. In a somewhat older individual, the majority of the germ 

 cells (Fig. I, PI. I) are much larger and now completely fill up 

 the halves of the small testis. They are, in size and general 

 appearance, like a great number of cells always found within 

 the testes of mature individuals, and are undoubtedly an early 

 generation of spermatogonia. In similar female polyps, the 

 corresponding germ-cells are always larger and are not so 

 closely crowded together. Comparatively few cells are in 

 division. The majority, as appears from the figure, remain for 

 considerable periods in the resting stage, and may be every- 

 where recognized by the large size of their nuclei in relation to 

 the cytoplasm, the lightly staining chromatin reticulum, and 

 finally by the presence of a pair of deeply staining plasmosomes 

 or nucleoli. These arise very early near opposite points on the 

 nuclear membrane as small bodies and increasing in size, make 

 their way to the center of the cell where they fuse into one 

 larger and more irregular mass. 



With the increase in the size of the testis, it is quite clear, 

 from the several sizes of the cells, that there are several genera- 

 tions of spermatogonia. The largest, which predominates, is 

 in all respects like the first generation of spermatogonia 

 observed in the above Fig. i. It is therefore clear that in the 

 transition between these two stages only a few of the early cells 

 divide at one time to give rise to the later generations. This 



