No. 2.] ANURIDA MARITIMA. 223 
(Fig. 4). This associated mass ultimately becomes the egg, the 
protoplasm containing the nucleus forming the definitive ovum 
and the surrounding cells bearing the relation of nutritive cells. 
Of the latter there are usually from five to eight grouped round 
one ovum; in the early stage they are not distinguishable from 
the general mass, but at a certain time an increase in size 
and also in the proportionate amount of chromatin is marked. 
This, together with the simultaneous decrease in size and 
change in shape and in amount of chromatin of the ovum 
nucleus, serves to emphasize the suddenness of differentiation. 
Fig. 10 shows the characteristic position of the ovum sur- 
rounded by a semicircle of nutritive cells. The change in the 
appearance of the chromatin can readily be seen by comparing 
Figs. 2,9, and 10. In Figs. 2 and 9, the youngest stages, the 
chromosomes are rather small, irregular masses on the periphery, 
usually eight in number, with a more centrally placed nucleolus. 
In the later stage (Fig. 10) the chromosomes have assumed 
a stellate structure of a most pronounced type; they are usu- 
ally eight in number with a more central and non-stellate 
nucleolus. In the same figure there is an additional change. 
There appears in the cell body close to the nucleus a mass of 
material clearly of a distinct chemical nature. It forms a cap, 
as it were, on one side of the nucleus, usually the side next to 
the ovum; by its accumulation it pushes the nucleus out of its 
hitherto central into an eccentric position. The presence of 
this material in the nutritive cells indicates a young stage in 
the ovum; yolk has not yet appeared in any large quantities. 
One more point must be noticed in this connection. There 
is always associated with the nutritive cells, usually one on 
each end of the string, a cell of distinctly different character. 
This is shown at a.o. in Figs. 10 and 11. It entirely lacks the 
characters of the nutritive cell. It is smaller, has an extremely 
small cell body and large nucleus with eight minute chromo- 
somes, which are at first arranged on the periphery, as is the 
case with the nutritive cell. There are one or two large 
nucleoli easily distinguishable from the eight chromosomes. 
Later the chromosomes move inward and arrange themselves 
in groups of four (Fig. 13). These cells have without doubt 
