124 ANATOMY AND PHYSIOLOGY 



tion of the sponge; and this idea appears the more feasible, 

 as these spicula are never observed in the inter-marginal 

 cavities, where the decomposition of animal matters would be 

 offensive to their especial function, but always in the spaces 

 beneath them, which are the commencements of the diges- 

 tive system. 



The same course of reasoning will apply to their occur- 

 rence in such considerable quantities amidst the defensive 

 fasciculi of spicida projected from the surface of Tethea 

 simillima, Bowerbank, MS., and also of T. crania, the latter 

 being represented by Fig. 362, c, c, Plate XXXI, in which it 

 will be seen that the recurvo-ternate heads of the spicula 

 are always situated beneath the level of the true defensive 

 spicula. Thus situated they would form an admirable trap 

 for the entanglement of soft annelids that might attempt to 

 crawl over the surface of the sponge, and thus they would 

 be destroyed and retained for the imbibition of their parti- 

 cles liberated by their gradual decomposition. If this be 

 not their especial purpose in this situation, I must confess 

 myself at a loss to imagine their proper function, as the 

 surface of the sponge is effectually protected by the por- 

 recto-ternate and large acuate spicula that compose the 

 defensive fasciculi projecting in such abundance from all 

 parts of the sponge. If we also consider the structure and 

 positions of the ordinary forms of internal defensive spicula, 

 the entirely spined attenuato-acuate ones, in reference to 

 the idea of their being offensive as well as defensive organs, 

 we shall not fail to see that, although less striking in their 

 forms and modes of disposition than the spicula already 

 described, they are calculated to subserve the office of 

 retaining prey quite as effectually as the more singular 

 ones. The abundance in which they occur, the vast 

 number of spines with which they are covered, the apices 

 of which are frequently long and recurved, combined with 

 the mode in which their bases are attached to the fibres of 

 the skeleton, exhibiting a beautiful combination of strength 

 and flexibility, are strongly indicative of a purpose beyond 

 that of mere repulsion. 



In the two species of sponges in which are found the 



