10 Mr. II . J. Carter on the Anatomy 



with " proper spicules " ; that is, the latter have only one end 

 fixed in the surface of the fibre, or otherwise, being in the 

 core, project through the fibre to a considerable extent. Thus 

 the core of the fibre may consist of one form of " proper 

 spicules " and the echination of another ; or the form of the 

 spicule a little modified may be the same in both ; or the core 

 may consist of foreign objects together with an echination of 

 " proper spicules," as before stated. 



Finally, the core may be generally or partially continuous 

 (that is, interrupted). 



Extremities of the Fibre. 



The basal or radical ends of the fibre are of course fixed to 

 the rock or other hard object on which the sponge may be 

 growing, or projected into the sand or mud at the bottom of 

 the sea, as the case may be ; so that it is with the circum- 

 ferential ones that we are now chiefly concerned. 



The circumferential ends may terminate in simple anasto- 

 mosis on a level with the surface ; or the larger fibre may 

 project in attenuated tag-like conical ends permeated respec- 

 tively by a single horny hair-like filament, or filled with an 

 axis of foreign bodies and surrounded by a dense anastomosis 

 of simple small fibre, which, branching off into a more open 

 reticulation at the circumference or base of the cone, joins 

 that of the neighbouring tags. Or the tags may present 

 themselves in the form of spines filled with an axis of 

 " proper spicules " instead of foreign bodies — or in the 

 form of monticules cored with one or more large spicules, 

 which thus form the axis, and project a considerable distance 

 beyond the summit like a hair or bunch of hairs. Or the 

 large fibre may end in a dermal reticulation which may be 

 surmounted by naked tufts of " proper spicules " that, when 

 large, come into contact Avith each other and thus form a 

 continuous incrustation more or less densely hirsute. 



Such are the usual modes of termination ; but of course they 

 are subject to great modification. 



Sponges with no Skeleton. 



In some sponges, as before stated, there is no fibrous 

 skeleton, and no apparent agent of support beyond the den- 

 driform canal-system and the spicules ; while in others there 

 is not only no fibre, but also no spicules, nothing but the 

 sarcode and the dendriform canal-plexus. 



