42 2 MONTGOMERY. [Vol. XV. 



a yolk substance, either of the yolk-ball fragments or a sub- 

 stance equivalent to that out of which the latter are differen- 

 tiated, and this substance, then penetrating osmotically the 

 nuclear membrane, becomes deposited or precipitated in the 

 nucleus in the form of spherical globules, which are the nucleoli. 

 From this yolk substance taken into the nucleus the chroma- 

 tin, linin, and nuclear sap might derive the nourishment neces- 

 sary for their growth, and those nucleoli which remain through 

 the fourth nucleolar stage might represent either a reserve supply 

 of this nourishment, or chemically changed portions of it, from 

 which all nutritive substances have been extracted ; the latter 

 view would seem substantiated by the fact that the nucleoli 

 stain somewhat differently in the third and fourth stages. 



The nuclear membrane is present during all these stages. 

 The nucleus is always regular in outline, usually oval, e.xcept 

 during the third stage, when it may become slightly irregular, 

 though it never becomes noticeably lobose or amoeboid. 



In the first nucleolar stage (Figs. 140 and 141) the chromatin 

 appears as a network of delicate fibers, which stain with haema- 

 toxylin. Towards the end of the second stage (Figs. 146-150) 

 it assumes the form of irregular masses, and the fibers become 

 less numerous. In the largest ovarial nuclei (Figs. 154 and 

 157) it is finely distributed throughout the nucleus in the form 

 of minute microsomes ; traces of fibers may be found only at 

 the periphery of the nucleus, though I have not determined 

 whether these are fibers now for the first time forming, as is 

 the case in the other nemerteans. The nucleoli are never 

 suspended by the chromatin fibers. 



This species is characterized by the formation of a mem- 

 branous structure in the cytoplasm, during the second and 

 third nucleolar stages, which is present in none of the other 

 nemerteans. This is a membrane within the cytoplasm, 

 separated from the nucleus, as well as from the cell membrane 

 by cytoplasm; it lies close to the nucleus (Figs. 146 and 155, 

 Iv. Mb.). It is thicker than the nuclear membrane, though 

 not so dense, and differs in no wise structurally from the 

 cytoplasm, except in its greater density, the cytoplasmic gran- 

 ules in it lying" closer together (these granules appear to be 



