OF THE SPONGIAD^:. 123 



interstitial cavaties of sponges thus armed without extreme 

 injury from the numerous points of these spicula, and every 

 contortion arising from its struggles to escape from its pain- 

 ful and dangerous entanglement would contribute to its 

 destruction, and it may then by its death and decomposition 

 eventually become as instrumental to the sustentation of 

 the sponge as if actually swallowed by the animal. How 

 far this mode of mitrimentation may obtain in the physiology 

 of these creatures it is impossible, in the present imperfect 

 state of our knowledge of their habits, to say, but from the 

 complex, varied, and elaborate structure of these organs, and 

 from their evident adaptation to retain such intruders, 

 as well as to defend the internal surfaces from injury, it is 

 not improbable that their office extends beyond that of the 

 mere defensive function, and that they are in fact auxiliary 

 organs for securing nutriment for the use of the sponge. If 

 this supposition, that the elaborately formed and ingeniously 

 disposed recurvo-quaternate spicula combine the office of 

 securing prey with that of defending the interstitial organs 

 of the sponge, be correct, it may afford a clue to the organic 

 purpose of the recurvo-ternate spicula with the exceedingly 

 long and attenuated shafts that so frequently accompany 

 the stout patento-ternate ones in Geodia Barretti. The 

 apices of these spicula (Fig. 54, Plate II) rarely attain the 

 height of the plane of the true connecting spicula, and their 

 recurved radii are most frequently projected into the large 

 interstitial spaces immediately beneath the plane of the 

 proximal ends of the cells of the intermarginal cavities, and 

 may thus form subsidiary defences to those organs. Although 

 emanating from the fasciculi of the shafts of the true con- 

 necting spicula, their form, slender proportion and position 

 evidently indicate a different office from the spicula with 

 which they are associated, and no other purpose for them 

 occurs to me so probable as the one I have suggested above. 

 Or we may carry the supposition further, and believe them 

 to be not only defensive but aggressive organs ; also, like 

 the recurvo-quaternate spicula, their office may be to retain 

 soft annelids that have intruded themselves through the 

 oscula into the digestive organs, to aid in the nutrimenta- 



