Miscellaneous. 229 



the external protoplasmic layer passes entirely to one side, forming 

 a sort of cap upon each sphere. The division into sixteen then 

 takes place, in such a way that the eight caps separate to form 

 eight spheres of protoplasm, side by side with the eight spheres of 

 fatty emulsion. From this moment the formative vitellus is com- 

 pletely separated from the eight large spheres of nutritive vitellus. 

 In Eschscholtzia cordata the latter is never composed of more than 

 sixteen spheres ; the former alone continues to become rapidly seg- 

 mented, and the nuclei suddenly make their appearance when the 

 small spheres have reached the number of thirty-two. In other 

 species the spheres of the nutritive vitellus continue to multiply by 

 division for a certain time, but always more slowly than the formative 

 vitellus. 



The formative vitellus is now juxtaposed to the nutritive vitellus ; 

 but when its cells have become greatly multiplied, it gradually en- 

 velopes the latter. The egg then reacquires precisely the appear- 

 ance which it had before the commencement of evolution. We may 

 distinguish in it, in fact, a central mass in the form of an emulsion, 

 the nutritive vitellus, and a peripheral layer, physically and chemi- 

 cally different. From this period, however, this layer is cellular ; 

 it is the blastoderm, or, if it be preferred, the external epithelium of 

 the animal. 



The mouth and intestinal canal soon make their appearance, in the 

 form of a tubidar invagination of the superficial epithelium. But, 

 without following step by step the formation of each organ, we shall 

 content ourselves with indicating two very remarkable histological 

 circumstances relating to the formation of the otolithes and that of 

 the tissue intermediate between the outer epithelium and the central 

 mass. 



The otolithes are formed in the embryonic nervous ganglion, which 

 only presents from thirty to forty cells. Each of them (originally 

 only one pair exists) appears as a little point in the interior of a cell 

 by the side of the nucleus. When it has acquired a certain size, it 

 slips out of the cell, this being the more easily effected because the 

 latter has no enveloping membrane. The author appears to be in- 

 clined to believe that all the otolithes are successively produced by 

 these two cells. 



The formation of the intermediate tissue is very curious. It is 

 effected by an actual secretion, with migration of cells. Between 

 the external cellular layer and the central mass there accumulates a 

 homogeneous, amorphous, and colourless substance. Stellate cells 

 are soon seen to detach themselves from the external layer and pe- 

 netrate into the interior of the homogeneous layer to constitute its 

 cellular web. The migration of these cells takes place by means of 

 their processes, which appear to act like the pseudopodia of the 

 Rhizopoda. 



M. Kowalewsky's memoir relates also to the development of Ces- 

 tiim, Pleurobrachia, Cijdippe, and Beroe, — Mem. Acad. Imp. de 

 St. Petersb. tome x. 186G ; Bill. Univ. 1867, Arch. Sci. pp. 24/- 

 249. 



