122 ANATOMY AND PHYSIOLOGY 



The faecal matters discharged by the oscula exhibit all 

 the characteristics of having undergone a complete diges- 

 tion ; whatever may have been the condition of molecules 

 of organized matter when they entered the sponge, their 

 appearance after their ejection is always that of a state of 

 thorough exhaustion and collapse. 



It is difficult to decide with any degree of certainty what 

 is really the nature of the nutriment of the Spongiadse, 

 but in the greater number of species it is probably mole- 

 cules of both animal and vegetable bodies, either living or 

 derived from decomposition. This appears to be the case 

 with the greater number of the Halichondroid sponges; but 

 even among them, as well as other genera, there are pecu- 

 liarities of structure that are strongly suggestive of car- 

 nivorous habits. Thus in the first portion of this paper 

 published in the ' Philosophical Transactions ' for 1858, p. 

 293, I have described among the interior defensive spicula 

 a remarkable form, which has been hitherto found in one 

 sponge only, the spinulo-recurvo-quaternate spiculum, 

 which " occurs in great profusion in the cavities of the 

 sponge, clusters of them consisting frequently of as many as 

 twelve or fifteen radiate from the angles of the reticulations 

 of the skeleton into the interstitial cavities of the animal." 

 I have also described, while treating on the internal defensive 

 spicula, the recurvo-ternate forms, the heads of which are 

 found projecting their radii, more or less, into the interstitial 

 cavities beneath the intermarginal ones in Geodia and 

 Pacliymatisma. The spinulo-recurvo-quaternate spicula, 

 represented in situ in Fig. 292, Plate XVIII, and the re- 

 curvo-ternate ones figured in situ in Pig. 354, Plate XXVIII, 

 e, e, are both admirably adapted to destroy the victims 

 entangled among them. 



I have for a long time entertained the idea that these 

 elaborate and varied forms of defensive spicula, probably 

 subserved other purposes than that of the protection of the 

 digestive surface against the incursions of minute annelids 

 and other predaceous creatures. They are admirably fitted 

 to retain and make prey of any such intruders. No small 

 animal could become entangled in the sinuosities of the 



