196 MORGAN. [Vol. IV. 



Cynthia ocellata, Cynthia partita, Ascidia amorpha, Molgula 

 manhattensis, Perophora viridis, Amanscium stellatum, and 

 Clavellijia sp. ? 



Finally, during the summer of '90, a new method of preparation 

 was obtained, which confirmed, from another point of view, the 

 previous results, and helped to make clear the exact origin of 

 the test-cells. 



Cynthia ocellata. — The ova are arranged around a central 

 cavity, which is the body cavity according to Van Beneden. 

 This cavity, which communicates by a duct with the atrial 

 cavity, is lined by a germinal epithelium, within which the ova 

 originate. 



In sections through the ovary, nuclei are seen lying along the 

 wall of the cavity of the ovary ; and here and there one is seen 

 to have enlarged, and the protoplasm about it to have increased 

 in quantity. This nucleus and protoplasm form the commence- 

 ment of a new egg. Such a condition is shown in Fig. i, 

 PI. VIII. At the periphery of this young egg another nucleus 

 is seen. This nucleus is one of those peripherally lying nuclei 

 which go to form the follicular nuclei of the Qgg. In Fig. 2 

 we see an older stage : at /" is a nucleus of the forming follicle 

 with its protoplasm stretching over the surface of the egg. 

 Other and similar nuclei lie around the Qgg in other sections of 

 the series. The follicular protoplasm surrounding the egg is 

 not a continuous mass, but is split up into cells corresponding 

 in number to the follicular nuclei. The cell walls are so 

 extremely thin that at this stage they cannot be seen in such 

 sections. 



Passing to a later stage, as shown in Fig. 3, the egg is 

 seen while enlarging to have pushed inwards from the germi- 

 nal membrane, which is still, however, attached to one side of 

 the &gg. 



The peripheral zone of protoplasm of the follicle is much 

 wider than in the last figure, and now is seen clearly to cover 

 the whole surface of the egg. Four follicular nuclei are seen 

 in this section. The nucleus of the ovum has also enlarged, 

 and contains in the figure a single large nucleolus. 



Fig. 4 is part of an Qgg of Cyjithia partita (hardened in picro- 

 acetic acid). The follicular zone is wider than in the last 

 figure, and the follicular nuclei are a little larger. The egg 



