OF THE SPONGIAD^. 119 



that while amidst the numerous specimens of Hymeniacidon 

 caruncula and Halichondria panicea that covered the rocks in 

 the neighbourhood of St. Catherine's Cave the former rarely 

 exhibited an open osculum in the absence of the water, 

 those of the latter species were frequently more or less 

 open. 



The most beautiful and striking view of the differences 

 existing between vigorous action, and the comparative repose 

 of the breathing process is exhibited in Grantia ciliata. In 

 this species the pores are situated on the obtusely conical 

 distal terminations of 'the intermarginal cells or cavities, each 

 of which is furnished with a long fringe of spicula surround- 

 ing its porous end (Fig. 346, Plate XXVI), their proximal 

 terminations being cemented, for about a third of their 

 length, to the slightly curved surface of the base of the cone. 

 In the state of the comparative repose of aerating inhala- 

 tion, and when the base of the conical extremity of the 

 cavity is not distended by the incurrent action, these spicula 

 all converge to a point- at the level of their own apices, and 

 the water thus gently inhaled passes between the shafts of 

 the spicula, forming the protective cone to the inhalent pores 

 and effectually preventing any extraneous matter from 

 approaching them. But when the vigorous feeding action 

 commences, the distention of the base of the conical portion 

 of the cavity brings it into lines parallel to the axis of the 

 cell, and thus the conical fringe of spicula assumes a cylin- 

 drical form, and the molecular food of the animal is freely 

 admitted to the pores. 



A corresponding action obtains in the exhalant system 

 of this interesting sponge. The mouth of the great central 

 cloaca is- furnished with a thick fringe of very long and 

 slender spicula, which by the contraction of its sides near 

 the mouth are all brought to assume a conical form like 

 those appended to the inhalant cavities ; but when the in- 

 halant action is in vigorous operation, and the oscula are all 

 pouring their streams into the cloaca, the force of the water 

 thus accumulated distends the mouth of the cloaca to such 

 an extent as to cause the fringe of long spicula to assume 

 the form of an open cylinder, or in some cases it is expanded 



