ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 283 



It is an encrusting sponge, growing on vegetable supports ; lias a 

 rpale flesh colour and a loose texture. The skeletal spicules are covered 

 with small spines ; flesh spicules are absent, unless small amphioxes 

 belong to this category. Spicule fibres are poorly developed ; in the 

 deeper parts the spicules generally lie irregularly disposed in the tissues ; 

 there is very little spongin. 



The gemmules are numerous, but are not aggregated in groups ; they 

 occur — each in a cavity of its own — both near the surface and deeper 

 down. They are oval, and have an opening like that of a bottle, ob- 

 structed by a chitinous septum. They are provided with a thick and 

 well-developed coat, in which amphidiscs of equal lengths are arranged 

 in a single layer. The shaft of the amphidiscs is furnished with conical 

 spines, large in size and situated at right angles to the longitudinal axis. 

 The outer surface of the discs is convex, and the margin is slightly 

 serrated. Amphidiscs in all stages of development are scattered about 

 in the sponge tissue where they are formed. 



Four classes of cells, each of which is derived independently from 

 the sponge, take part in the formation of the gemmule ; first, the mother- 

 cells of the yolk-cells which alone constitute the reproductive portion 

 of the gemmule ; secondly, the mother-cells of the columnar cells, which 

 pass back to the sponge ; thirdly, the mother-cells of the amphidiscs, 

 " scleroblasts," which become modified and form a part of the intermediate 

 layer of the protective coat of the gemmule ; and fourthly, the tropho- 

 cytes, whose function is to supply both the columnar and the yolk-cells 

 with food-material, and which, like the columnar cells, pass back to the 

 sponge. 



The yolk-cells and the columnar cells draw their food-material in 

 solution from the trophocytes ; the yolk-cells store it up as a reserve in 

 the yolk-bodies ; the columnar cells use it in such a way as to enable 

 them to secrete the inner chitinous layer, to grow and pass out between 

 the outer ends of the amphidiscs, their inner ends being modified to 

 form the greater part of the ground substance of the protective coat of 

 the gemmule, and finally, to secrete the outer chitinous layer ; processes 

 which mean that there is an enormous amount of metabolism going on. 

 The amphidiscs are developed in cells, the scleroblasts, which carry them 

 through strands of the sponge tissue to their ultimate position in the 

 protective coat of the gemmule. 



The above is the author's summary of his general results. His com- 

 munication ends with a critical review of previous researches, and 

 opinions on the formation of gemmules. 



Antarctic Sponges.* — E. Topsent makes a preliminary note on the 

 sponges collected by the Belgian Antarctic Expedition. Twenty-six 

 species were obtained : — Calcarea (2), Monaxonida (13), Carnosa (1), 

 Hexactinellida (9), Halisarcida (1), Monoceratina (0), Tetractinellida 

 (0) — and thirteen were new. 



* fcThere is little resemblance to Arctic forms. The author notes 

 that Leuco8olenia lamarcki, Halichondria panicea, and Dendoryx incrustans, 

 which are common to both, are really cosmopolitan. The abundance of 

 Hexactinellids — alike in species and individuals — is characteristic of the 

 South. 



* CompteB Rendus, cxxxii. (1901) pp. 168-9. 



