440 MONTGOMERY. [Vol. XV. 



Germinal vesicles, nucleoli. — In this genus the earliest egg 

 stages are more favorable for study than in the other metane- 

 merteans. In the connective-tissue nuclei from which the ger- 

 minal vesicles are directly derived (with no intervening cell 

 generations) no nucleoli are present, though this conclusion was 

 possible only after much careful observation. These small 

 nuclei (Figs. 213, 217, 218, 220, 228, C. T. N.) are character- 

 ized by a relatively thick membrane and by chromatin which is 

 usually granular in distribution, but which may sometimes 

 occur in the form of granular fibers. These chromatin masses 

 might at first sight be confounded with nucleoli, but their small 

 size and irregular contours show that they are true chromatin 

 granules. Further, when these nuclei are stained by the 

 Ehrlich-Biondi method, these fibers and granules always stain 

 with methylen green (chromatin reaction) and not a single one 

 stains with fuchsine (which invariably stains any true nucleoli). 

 Accordingly, what could not be finally proved for the other 

 metanemerteans, though all observations pointed to its being 

 the case there, could be definitely settled for Stichostetmna, 

 namely, that these connective-tissue cells contain no nucleoli ; 

 in other words, nucleoli first arise in the definite germinal 

 vesicles. 



Before proceeding to the description of the egg cells it may 

 be noted that not all the undifferentiated connective-tissue 

 cells within the gonad become germinal vesicles, I have previ- 

 ously ('95) shown that the young gonad is a cell syncytium in 

 which numerous nuclei are unevenly scattered through a mass of 

 cytoplasm, but cell boundaries cannot be seen (Figs. 2 1 7 and 2 1 8). 

 A few of these nuclei increase in size and eventually become 

 germinal vesicles, and the latter reach maturity not simultane- 

 ously but in succession, so that no gonad contains more than one 

 large ovum at a given time. The numerous other nuclei which 

 do not become thus differentiated degenerate, and their sub- 

 stance is eventually absorbed by the gradually increasing mass of 

 cytoplasm of one of the growing egg cells. These regressive 

 processes are as follows (Fig. 218, C. T. N.) : the nuclei 

 increase a little in size, but become much clearer in appearance, 

 i.e., the relative amount of their chromatin appears to decrease ; 



