Classification of the Spongida. 127 



without this aid. So that, after all, we may be thrown back 

 upon structural peculiarities in combination with general form, 

 and perhaps sometimes colour, for ultimate distinction. (This 

 will be found to be particularly the case with the Hircinida.) 



Still there are many instances where the same species may 

 be hastily recognized by its outward features ; but as this 

 can only be done after much experience, it is of no use to a 

 beginner. At the same time, from what has been above stated, 

 it would always remain uncertain, even to the experienced, 

 without a microscopical examination. 



A fresh sponge, too, described in its natural state (that is, 

 with the sarcode on) differs greatly from that in which the sarcode 

 is off, or where the skeleton only remains. As, however, by far 

 the greater number of sponges come to us in the latter state, and, 

 indeed, all must be divested of the sarcode before they can be 

 usefully described for classification, seeing that, as before 

 stated, there is no animal expression (so to term it) externally 

 or internally that can be made use of for this purpose, it 

 seems best to describe the skeleton naked, rather than under 

 cover of the sarcode — that is, to describe the skeleton only, 

 although, of course, where this can be done with the sarcode 

 on as well as off it is best of all. But there is no doubt 

 that a description of the sponge with the sarcode on will 

 never serve to recognize its skeleton, which is at once the 

 most characteristic and frequently the only part that we 

 can or are ever likely to obtain from the inaccessible loca- 

 lities in which many grow ; so after all we are not so 

 badly off with the skeleton only, provided it has not been 

 worn away by much attrition. Hence the fundamental divi- 

 sions of my arrangement will be based on the characteristic 

 features presented by the elementary composition of the skeleton 

 or organ of support. It should not be forgotten, however, that 

 with the sarcode of course the flesh-spicules disappear, falling 

 through the skeleton, as before stated, like small pebbles 

 through the meshes of a fishing-net, when the sarcode passes 

 into dissolution. Nor should it be forgotten that there may 

 be a great difference between a sponge in its " fresh " and 

 in its dried state, in size, colour, and general appearance. 

 As the sarcode in all assumes the characters of glue when 

 dry, those which, like the Carnosa, are without horny 

 skeleton can only be described when fresh or preserved in 

 some aqueous solution. Also sponges possessing a skeleton 

 sink down in many instances to half their original size by 

 the shrinking up of the sarcode, which, clinging round the 

 skeleton, destroys the original plumpness of the sponge, and 



