18 A MONOGRAPH OF THK 



Colour. — Cream white. 



Habitat. — Nearly all parts of the British coast ; littoral, 

 or parasitical on fuci to 8 or 10 fathoms deep. 

 Examined. — Alive. 



This sponge varies exceedingly in size and shape. In 

 the young condition it is usually more or less of an elon- 

 gated oval form, having a single mouth to the cloaca, at 

 the distal end of the sponge. In older specimens it ex- 

 pands laterally to a very considerable extent, becoming 

 irregularly foliaform and angular at the margin, and at each 

 angle there is usually a mouth to the cloaca. When left 

 by the tide, or in a state of repose, the sides of the sponge 

 are in close contact, and the mouths of the cloaca are 

 closed, but when immersed in water and in full action the 

 sponge becomes considerably distended, and the excurrent 

 streams issue with much force from the mouths of the 

 cloaca. The largest specimen of this species I have seen 

 was collected from the Ipswich River by Dr. W. B. Clarke. 

 It was five in length, and its greatest breadth three and a 

 quarter inches, although of this comparatively enormous size 

 the interstitial cells of the sponge differed very little in their 

 proportions from those of the species of an ordinary size 

 Their diameter did not appear to be in any appreciable 

 degree increased, but their length was nearly double that of 

 the cells of an ordinary sized specimen of the same species. 



The oscula at the proximal t(jrmination of the interstitial 

 cells are grouped two or three together at the bottom of 

 irregularly shaped depressed areas, formed by a compact 

 network of triradiated spicula and membranous tissue. 



The margins of these areas are often furnished with 

 spiculated triradiate spicula, the spicular rays being pro- 

 jected most frequently at a sUght inclination towards the 

 mouth of the cloaca, forming to a certain extent a defensive 

 system against intruders within that space, but they are 

 not, as might be expected from the collapsing habit of this 

 sponge, of any great length. 



The exhibition beneath the microscope of the pouring 

 forth of the excurrent streams from the oscula of this 



