BRITISH SPONGIADiE. 21 



dried these conical papilla? are transformed into dense 

 pencils of long spicula, and the whole sponge assumes a 

 very hirsute appearance. The bundles of spicnla are often 

 seen, in the dried specimens, reclining on the surface of 

 the sponge in every imaginable direction. The cloaca 

 in young specimens is often disproportionately narrow, but 

 in adults it is sometimes one third the diameter of the 

 sponge in width ; it is narrowest near the base of the 

 sponge, and gradually enlarges towards its apex. 



As the sponge has evidently a considerable amount of 

 expansile and contractile powers, these differences in the 

 diameters of the cloaca may in many instances depend on 

 whether the animal had died in a fully distended or a 

 completely contracted condition. 



The spiculated triradiated spicula with which the interior 

 of the cloaca is armed are not very numerous, and the 

 points of the defensive rays are usually directed more or 

 less towards the distal end of the sponge. 



The mouth of the cloaca is profusely furnished with the 

 long defensive acerate spicula ; they are very slender and 

 flexible, and often exceed the eighth of an inch in length. 

 At the insertion of their bases into the curving termination 

 of the sponge there is intermingled with them a consider- 

 able number of stout, short, fusiformi-acerate spicula, which 

 renders that portion of the spicula forming the ciliary 

 ring quite inflexible, so that when the mouth of the cloaca 

 is distended by the force of the excurrent stream the ciliary 

 spicula, which in the quiescent state of the sponge were all 

 converging towards its axial line, are now by the distension 

 of the mouth of the cloaca carried into positions, which 

 often exceed those of lines parallel to the long axis of the 

 sponge. The action of the separation or approximation of 

 the distal points of the long defensive spicula is, therefore, 

 simply due to a wise and beautiful mode of insertion into 

 the distal termination of the sponge, and their motions are 

 in no degree dependent on muscular action. 



Besides the spicular defences of the mouth of the cloaca, 

 I have in two cases found a tense membrane at the base of 

 the neck of the cloaca! orifice, entirely closing it, and this 



