176 ANATOMY AND PHYSIOLOGY 



struct the generic characters so as to endeavour to limit 

 the genus within definite bounds. I propose therefore to 

 substitute the following characters for those of the French 

 authors. 



Alcyonckllum, Quoy et Gaimard. 



EuPLECTBLiA, Oaen. 



Sponge fistulate ; fistula single, elongate, without a massive 

 base. Skeleton : primary fasciculi radiating from the 

 base in parallel straight or slightly spiral lines ; secon- 

 dary fasciculi at right angles to the primary ones. 

 Oscula congregated, with or without a marginal 

 boundary to their area. 



Tjrpe, Alcyoncellum corbicula, Quoy et Gaimard. 



The congregation of the oscula in Alcyoncellum corbicula 

 and aspergillum is not a character peculiar to those sponges. 

 A similar mode of arrangement exists in several species of 

 Geodia. In G. gihherosa, in the Museum of the Jardin 

 des Plantes at Paris, they are congregated in an area with 

 a well-defined boundary, and in specimens of G. Barretti 

 in my possession they are situated in deep depressions or 

 cavities on the surface of the sponges ; and these cavities 

 or areas are not uniform in either shape or size ; so we may 

 infer that the presence in some species of Alcyoncellum of a 

 well-defined marginal boundary to the oscular area, and its 

 absence in other species, amounts to a specific difference 

 rather than to a generic distinction ; but in either case the 

 oscular are congregated at the distal extremity of the 

 sponge, and the areas of its parietes are the inhalant por- 

 tions of the animal. The inhalation and exhalation of 

 water is precisely on the same principle as that which 

 obtains in Grantia ciliaia ; the whole of the parietes are 

 appropriated to inhalation, the incurrent streams are passed 

 through the interstitial cavities and discharged into a com- 

 mon cloaca, and the effete stream ejected at the distal 



