SMALLWOOD : MATUEATION OF HAMINEA SOLITARIA. 265 



The cytoplasm of a young ovocyte presents a granular appearance 

 which is perfectly uniform in all regions of the cell (Plate 1, Fig. 2). 

 I have tried several plasma stains, but have been unable to demonstrate 

 a yolk nucleus, such as Crampton ('99) finds in Ascidians, and others 

 have found in other animals ; nor do I find that the surrounding cells 

 are taken into the cytoplasm as in Helix (Obst, '99). The egg simply 

 increases in size, this increase being accompanied by the appearance of 

 deutoplasmic bodies in the cytoplasm, which at first are few and small. 

 After these yolk spheres have begun to be formed, they increase rapidly 

 in number, until there is no evidence of any substance outside the 

 nucleus and inside the egg membrane except deutoplasmic bodies. 



The changes which take place in the nucleus can be easily observed. 

 In the young ovocyte the nucleolus is a solid mass staining uniformly 

 (Fig. 2). From it there often radiate more or less regularly arranged 

 linin fibres, which give to the nucleus a radiate appearance. As soon as 

 the deutoplasm begins to appear in the cytoplasm there can be distin- 

 guished in the nucleolus clear regions (Fig. 3), at first very minute, after- 

 wards larger and usually round ; these vacuoles increase in size and 

 number, adjacent ones fusing into larger vacuoles, and these eventually 

 uniting into one large cavity, such as are shown by Montgomery ('98) 

 for Piscicola rapax and Tetrastemma elegans. During the growth of 

 the egg, the nucleus increases in size proportionately to that of the whole 

 egg. Owing to the increase in the size of the nucleus, it is difficult to 

 say whether in the early stages the stainable material of the nucleolus is 

 disappearing, or whether the nucleolus is simply enlarging and the added 

 space is being occupied by the fluid in the vacuoles (Plate 1, Fig. 3 ; 

 Plate 2, Fig. 7). However that may be, as the egg begins to reach full size, 

 the nucleolus becomes filled with a non-staining fluid, the dark staining 

 portion diminishing and finally disappearing. It has not been possible 

 to demonstrate any structure in the vacuoles of the nucleolus ; this agrees 

 with the observations of Korschelt ('95) on Ophryotrocha and Mont- 

 gomery ('99) on Piscicola and Tetrastemma, but differs from those on 

 Tubifex rivulorum and Clepsine complanata by Gathy (:00), who finds 

 a definite network in the nucleolus at a corresponding stage. Coe ('99, 

 p. 436) finds in Cerebratulus also a network in the vacuole. The vacuoles 

 in the nucleolus of Ophryotrocha, as observed by Korschelt ('95, pp. 562- 

 573), are in the early stages similar to those in Haminea, but in Ophryo- 

 trocha they do not fuse into one large structure occupying the whole 

 of the nucleolus. 



As compared with the young ovocyte, the full-grown egg (Plato 1, 



