OF THE SPONGIAD^. 161 



A careful examination of the British species of this 

 Order will very soon satisfy a naturalist that there are at 

 least four distinct forms in the organization of the skeleton, 

 and that each is fully entitled to generic distinction. Thus 

 in Grantia ciliata and compressa, Johnston, we find the 

 sponge to be constructed of a series of cells, each having 

 separate parietes, and extending from the dermal surface to 

 near the inner surface of the sponge, where they discharge 

 the faecal streams into a common cloacal cavity. In 

 Grantia hotryoides, Johnston, the system of cells is entirely 

 wanting ; the sponge is composed of a single thin stratum 

 of membranous structure and spicula, surrounding a large 

 cylindrical cloacal cavity, from the terminations of which 

 the faecal streams are discharged. In Grantia nivea, John- 

 ston, we find the sponge massive and irregular in form, 

 containing numerous capacious cloacal cavities, each termi- 

 nated by a single large ' mouth, the interstitial structures 

 between the sides of these great cavities and the dermal 

 surfaces of the sponge consisting of irregularly disposed 

 membranes and spicjila, permeated by contorted interstitial 

 cavities, terminating in simple orifices or oscula in the sides 

 of the great faecal cavityyinto which they discharge their 

 excurrent streams ; and in Leucogypsia Gossei, Bowerbank, 

 the sponge is massive, without cloaca, fornied of irregularly 

 disposed, membranous tissues and spicula, and with oscula 

 at the external surface, thus simulating to a great extent 

 the mode of structure of the Halichondroid tribes of 

 sponges. '. 



The sponges of this Order appear to possess a high 

 degree of vital power, and I have rarely failed in finding 

 the excurrent orifices in vigorous action in either Grantia 

 compressa, ciliata, or hotryoides when recently taken from 

 the sea. In G. compressa, especially, I have often observed 

 the inhalant and exhalant actions remarkably vigorous; 

 and if a drop of water containing finely comminuted indigo 

 be mixed with the water in which they are immersed, they 

 wiirbecome deeply tinctured with it in a very few seconds. 

 This vigorous action is accounted for by the highly deve- 

 loped ciliary system, which may be readily seen in action 



