394 Mr. Hogg's Observations on the Spongilla fluviatilis, 



Sponge, which constitute the months or entrances to the wider passages or 

 canals formed in that structure by the anastomosing fibres, and wliich are 

 precisely similar to those seen in a number of the Marine Sponges, and have 

 been named by Dr. Grant the fœcal orifices, I have here called oscules {oscula), 

 — a term previously used by Ellis and Solander and by Pallas to designate 

 tliem, — because I consider the SpongilUv, being vegetable productions, cannot 

 possibly have any fœces to discharge. Although the ejcctamenta, or little 

 pieces of soil before alluded to, are principally the feeces not of the Spongilla, 

 but of certain animals parasitically nestling within it: these have been also 

 mentioned by Dutrochet, and described by him as " des fragmens de la matière 

 caséïforme :" they are usually of a brownish colour, and ai-e conveyed from 

 the canals with the expelled current of water. On placing a living specimen 

 of the Spongilla as naturally attached to a stone, or piece of wood, Sec. in a 

 basin of pure water, these ejectamenta may be in a little time perceived freshly 

 washed out of the canals, and resting on the surface about its oscules. They 

 are most conspicuous on looking at the Sponge in the morning (having on the 

 previous night changed the water), when the whole specimen is generally 

 covered by them, and is rendered quite dirty and discoloured. Washing the 

 Sponge, by letting some fresh water run over it, I again noticed after a few 

 hours more the same appearances. And on examiniug the specimen, I dis- 

 covered the presence of some insect or other animal, and found that these 

 ejectamenta were partly its excrementitious discharges, and partly bits of 

 broken fibres, and particles of the Sponge, which were loosened by the gnaw- 

 ing or burrowing of the same creature. I never observed these ejectamenta 

 upon any fresh specimen wlierein I was unable to detect any strange animal. 

 Much the same sort of brownish excrement I have seen as emitted by the nu- 

 merous polypes of Phimatella repens*, when I have kept them in a glass vessel 

 filled with water for the purpose of studying their habits and organization. 



Now, as to the fancied irritability, or powers of contraction and dilatation of 

 this species oi Spongilla, numerous experiments have convinced me that they 



* The like experiment of scattering some magnesia powder on the surface of tlie water wherein is 

 contained a little colony of these Zoophytes, will demonstrate, in the same way, that eddies and cur- 

 rents are in powerful action whenever any of the minute polypes have protruded themselves from their 

 membranous dwellings. See ante, p. 390. 



