208 ISAO lUIMA. 



both for the sake of giving a connected account of the same, 

 and for comparison with Ludwig's statements. 



A single germ-cell without a proper membrane, but 

 tolerably clearly outlined, enlarges, and its nucleus multi- 

 plies by division, thus producing a large multi-nucleated 

 mass or cell. Around one of these multiple nuclei a well- 

 defined area of clear protoplasm, separated from the remain- 

 ing protoplasm by an inchoate membrane, soon appears. 

 The primordial ovum thus formed assumes a spherical shape, 

 and the membrane gradually becomes double-contoured. 

 The ovum grows at the expense of the contents of the follicle, 

 crowding the free nuclei against the follicular wall as it 

 grows in size. 



The contents of the follicle enlarges at the expense of the 

 adjacent cells, which coalesce to form a protoplasmic mass, 

 with free nuclei around the follicle. Thus, the follicle with 

 its protoplasmic contents, the free nuclei and the ovum, all 

 arise from a single germ-cell. 



The follicle has no definite wall in the form of a layer of 

 cells, as in the case of higher animals, but represents simply 

 the area formed by the expansion of a single cell — an area 

 bounded by a hardened area of the elements of the egg- 

 string. 



The formation of the ovum of Nephelis is in one par- 

 ticular an abbreviated form of what occurs in Piscicola, In 

 both cases the whole series of events transpires within the 

 limits of a single cell. In Piscicola free nuclei are also 

 formed, but eventually these nuclei become the centres 

 of so many cells, while in Nephelis only one nucleus does 

 so, all the rest remaining free. In Piscicola one of the mul- 

 tiple cells becomes the ovum, while the others are absorbed. 

 The formation of cells in Piscicola, excepting the ovum, 

 would appear to be superfluous, and this part of the process 

 is skipped in Nephelis. According to Ludwig the germ- 

 cell in Piscicola produces a capsule, which, later, encloses 

 both the ovum and the remaining cells. Whether the egg 

 subsequently became enveloped by a special vitelline mem- 

 brane was left undecided. 



VI. The Archiamphiaster. 



With regard to the changes preliminary to cleavage in 

 the egg of Nephelis, we have the valuable observations of 

 Biitschli (No. 19) and O. Ilertwig (No. 8). In order to see 

 lor myself the interesting phenomena described by these 

 authors I have gone over the same ground, and have dis- 



