AND HISTOLOGY OF SPONGES. 231 



In the Hexradiate group before-mentioned, so named on account 

 of all its spicules being formed more or less on that type, we have 

 spicules in some cases of great length, extending from the base of 

 the Sponge, the ends of many terminating in booklets, often re- 

 minding one of anchors or grapnels, by which the Sponge attaches 

 itself to the bottom of the ocean in the mud, and is thus swayed to 

 and fro by the currents without injury to the main body. 



When the Hyalonema, or Glass Rope Sponge, was first brought 

 over from Japan, some few years back, it was believed for a long time 

 that the Sponge grew with the long-twisted coil of spicules upwards ; 

 'but from subsequent dredgings and further examination and inquiry, 

 it was found to be the contrary, and that it was the Japanese them- 

 selves who had imposed on our credulity, by imbedding the Sponge 

 in the cavities formed in stones, &c.,by some mollusc, with the glass 

 rope looking like so many long brushes of spun glass bristling 

 upwards. A specimen of these may be seen in the British 

 Museum. 



We have over two dozen recorded genera of British Siliceous 

 Sponges, so that it would be impossible for me to go through them 

 in one evening. ]\Iany of the spicules of some of them are familiar 

 objects in our cabinets, such as the stellate forms of Tetliya, the so- 

 called gemmules of Geodia and S pong ilia ; but I must leave that part 

 for a future time. 



The spicules which go to form the non-histological part of a 

 Sponge build up more or less the skeleton, excepting in the purely 

 Keratose ones. The forms they take in the Calcareous Sponges are 

 mostly of a tri-radiate type ; but in the Siliceous ones they take 

 forms, which for beauty and symmetry are often hardly to be equalled, 

 more particularly the minute spicules dispersed through the sarcode. 



The Keratose Sponges have in some cases their fibres strengthened 

 by the presence of spicules, generally of the acerate type. One 

 species of the latter, named Dysidea fragilis, which may be found 

 very plentifully at Brighton, seems to have a selective power of taking 

 up grains of sand, often about the same size, and depositing them 

 in its structure. In a specimen I have seen, evidently allied to 

 Dysidea, from Australia, in the possession of Mr Waller, the finest 

 hair-like fibres had grains of silex regularly arranged in their 

 interior. 



The true essential part of a Sponge is composed of structureless 

 sarcode and nucleated cells, placed side by side, with a flagellam, some 



