1901.] SOME ARCTIC NEMEBTEANS. 105 



othei's in stages fairly well advanced (Plate VI. fig. 5). Towards 

 the hind end of the body, however, earlier stages in the formation 

 of the ovary may be found. At certain spots within the copious 

 gelatinous connective tissue surrounding the intestine may be seen 

 a very young ovum (Plate VII. fig. 13), around which a space is 

 commencing to appear. The connective-tissue nuclei around this 

 space are somewhat more plentiful than in other parts. The 

 ovum at this stage is surrounded by a small amount of yolk- 

 material, though whether this represents its own protoplasm or 

 has been derived from other cells which apply themselves to it, I 

 am unable for certain to say. At a somewhat later stage the 

 cavity in the connective tissue has become larger, with a more 

 definite outline, whilst at the same time the ovum has increased 

 in size and is seen to be surrounded by cells (Plate VII. fig. i4) 

 composed mainly of yolk-material. In some of these cells is to 

 be found a well-marked nucleus and a nucleolus of similar staining 

 reactions to those of the ovum itself. In others the large nucleolus 

 alone can be recognized, whilst in others again all traces of both 

 nucleus and nucleolus have disappeared. It seems reasonable to 

 suppose that these cells are in reality primitive ova which apply 

 themselves to the functional ovum and become converted into yolk- 

 material around it. The ovum now increases greatly in size, and 

 the ovarian cavity becomes lined with a flattened epithelium 

 derived from the cells of the gelatinous connective tissue. This 

 epithelium may be traced passing over and covering the ovum 

 (vide some of sioallest ova in Plate VI. fig. 5), where it gives rise 

 to a peculiar coat of follicle-cells. The follicular layer takes the 

 form of a layer of irregular-shaped cells, with branched processes 

 on the outer side, forming delicate strands connecting the ovum 

 with the adjacent ovarian wall or other follicle-cells, whilst on the 

 inner side are more regular processes like little waterspouts pro- 

 jecting through the delicate limiting membrane of the ovum into 

 the sea of yolk beneath (Plate VII. figs. 15 & 16). As the 

 ovum nears the ripe condition it becomes coated with a shell-like 

 structure. On the ventral surface of the ovum (^. e. on the surface 

 furthest from the dorsal opening of the ovary) the follicular layer 

 degenerates into an undulating homogeneous deeply staining 

 covering to the ovum (Plate VII. fig. 15). At the same time the 

 surface of the ovum in this region takes on a similar appearance. 

 This process gradually spreads round the ovum. Between the 

 two layers are small spaces which subsequently disappear, though 

 the two layers can still be recognized by the fact that the outer 

 takes on a far deeper stain, owing probably to its containing more 

 chromatin derived from the nuclei of the follicle-cells (Plate VII. 

 fig. 17). The outer egg-covering is undoubtedly derived from the 

 follicle-cells ; the inner layer is formed within the fine limiting 

 membrane of the ovum, though the material which composes it 

 has probably been derived also from the follicle-cells. The largest 

 ova observed were irregularly oval in shape, measuring about 

 700 X 420 {x. 



