ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 757 



The cemental Gastrseades fall into two groups, which have the 

 same relation to one another as have the Ascones to the Leucones 

 among the Calcispongife. In the simple and phylogenetically older 

 forms, the wall of the gastric tube is thin and solid, but in the 

 further developed it is thicker and traversed by gastric canals. The 

 former, allied to the already described Haliphysema and Gastrophjsema, 

 are either branched {Dendrophysema) or plexiform (^Clathrophysema). 

 The latter belong to a new group called the Cfementaria ; resembling 

 many Dysidiidae, they are distinguished by the complete absence of 

 ectodermal pores, so that the water only enters the irregular canal- 

 system (the spaces of which are completely or partly invested by 

 endodermal flagellate epithelium) by the mouth-orifices. In the 

 endoderm there are scattered ovarian cells. Ccementascus forms 

 simple tubes, with a single oral orifice ; Ccementoncus has several 

 orifices and is irregular in form ; Ccementissa forms flat lobate crusts ; 

 Ccementura branched creeping or dendriform masses with several 

 mouth-openings. Hackel thinks that the Orthonectida are allied to 

 the Cyemaria, and that the Trichojplax of F. E. Schultze is a perma- 

 nent Discogasirula form. 



Siliceous Spicules of Sponges.* — J. Thoulet has examined the 

 structure and other characters of the spicules of various sponges 

 collected during the last cruise of the ' Talisman.' They were 

 separated by treating the sponge with hydrochloric acid. The 

 acicular spicules lost 13 '18 per cent, of weight on heating to red- 

 ness for ten minutes in a platinum crucible. Before the blow- 

 pipe they were whitened, or became slightly ochreous in colour, 

 without a trace of fusion. Stellate spicules of five rays lost 12-86 per 

 cent, on calcination. The specific gravity, obtained by flotation in a 

 solution of iodides, was 2-032. But the spicules have a delicate tube 

 along the centre generally less than -001 mm. in diameter; and 

 allowing for this, the author obtained by calculation, 2-0361 as the 

 true specific gravity — which is that of opal. 



The spicules are easily attacked by difierent chemical agents, so 

 that they ought to be very readily dissolved in sea-water on the death 

 of the animal. They were analysed after calcination by Boricky's 

 process, by means of pure hydrofluoric acid, after first boiling in 

 nitric acid and calcining, and they were proved to be pure silica. 

 When not previously calcined, but simply washed, the process yielded 

 a residue of hydrofluosilicate of soda in hexagonal prismatic crystals, 

 the origin of which it is hard to explain unless it be that the minute 

 tube of the spicules contains sea-water. 



Fresh-water Sponges and the Pollution of River- water.! — E. 

 Potts has examined the sponges found in the forebay of the Phila- 

 delphia waterworks when the water was withdrawn, and considers 

 that the sarcode of fresh-water sponges does not slough ofi" at the 

 approach of winter, so that these organisms do not ordinarily pollute 



• Bull. See. Mineral. France, April 1884. Cf. Amer. Joura. Sci., xxviii 

 (1884) p. 76. 



t Proc. Acad. Nat. Sci. Philad., 1884, pp. 28-30. 



