ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 769 



and the thickness of the protecting mantle, which is here merely 

 a feebly developed hyaline layer, dex-ived from the ectoderm and 

 without any special cells. 



Development of Ganglion and Ciliated Sac in Pyrosoma.* — 

 The ciliated sac, or " olfactory organ," has been studied by L. Joliet 

 in the bud of this Tunicate. The walls of its canal consist of a 

 cubical non-ciliated epithelium, a few cilia and flagella occurring, 

 however, at the point at which it opens into the branchial sac ; the 

 median tubercle is composed of a mass of small round cells, grouped 

 round a diverticulum of the canal. The organ evidently represents 

 the canal of the gland of the Ascidians proper, the anterior ciliated 

 part corresponding to the " pavilion," and the median tubercle being 

 apparently a rudimentary gland.. Kowalewsky is wrong in speaking 

 of a cavity within the ganglion, and of the obliteration of the cavity 

 of the primitive neural canal, for he has mistaken the latter for the 

 ganglion. The canal is constricted at each point at which a young 

 bud is given off, and thus forms a pear shaped vesicle within each 

 older zooid, and its walls undergo modifications. From its hinder end, 

 which thickens, some round cells between the vesicle and the ectoderm 

 are detached ; these cells proliferate actively, and form an oval mass 

 which grows round the posterior end of the vesicle, constituting the 

 true ganglion in almost its adult form. The vesicle opens into a 

 depression in the branchial sac, and becomes the ciliated sac of 

 Huxley. Probably the neural canal of Ascidian larva? also, of which 

 the cerebral vesicle is a part, is only the rudiment of the canal of the 

 subneural gland. The function of the canal in question is probably 

 olfactory, a supposition favoured by its direct apposition against the 

 ganglion ; it is at any rate not excretory, as the ciliary currents set 

 towards the bottom of the sac and not towards the exterior. 



Development of Genital Products of Cheilostomatous Bryozoa.t 

 — W. J. Vigelius has found a very suitable object for study in the arctic 

 species Flustra membranaceo-truncata, where he finds that the ovary arises 

 from the inner surface of the endocyst, and from that portion of the 

 wall of the distal half of the zocecium which lies opposite to the side 

 which carries the operculum. Each ovary forms a small spherical or 

 ellipsoidal body of a yellowish colour, which consists of a number of 

 small, round, closely-packed cells. Although apparently isolated, it 

 is connected with the endocyst, the small cells of which take part in 

 its formation. A differentiation is soon seen in the primitively 

 similar elements, for two (or, rarely, more) become distinguished by 

 their size ; the other cells become set around these two ova, and the 

 growth of the latter is accompanied by an increase in the size of the 

 follicle, the cells of which apparently increase by division. When 

 the ovarian cells have attained a certain size, there commences a 

 struggle for existence. One grows more rapidly than the other, and 

 the less fortunate one is driven to the periphery of the ovum, where 

 it ceases to grow, although still quite distinctly an ovarian cell ; 



* Coniptes Bendus, xciv. (1882) pp. 988-91. 

 t Biol. Centralbl., ii. (1SS2) pp. 435-42. 



