141 



I afterwards examined ; but I often had two or three in the remains 

 of cells which I had thus laid open. 



I could not discern whether the cilia were based upon the tessel- 

 lated cells, or whether they sprung from between the,m ; but, from 

 their continual association with the cells when removed from the 

 body of the sponge, I am strongly inclined to the former opinion, 

 and the more so as the tessellated cellular structure does not occur 

 in any other portion of the sponge than that in which the cilia exist 

 and the motions of the currents originate. 



The situation and action of the cilia in this species fully explain 

 the powerful and continuous stream that issues from the great ex- cur- 

 rent orifice of the sponge, without the necessity for cilia in any other 

 part of the animal. 



From the existence of chambers, or cavities, immediately within 

 the in-current orifices of Halichondria panicea, and other similarly 

 constructed species, I am strongly inclined to believe that we must 

 look for the cilia in those parts only. 



I have frequently taken sections of a large ex-current canal, at 

 right angles to its axis, about the eighth of an inch in depth from 

 the surface of the sponge, while the currents were in action, and 

 have observed that the action continued, in the portion thus sepa- 

 rated from the body, ejecting a stream of water from the mouth of 

 the canal, for often half an hour after its separation ; and, that no 

 error might arise in the observation, I have always conducted the 

 investigation in a closed cell. 



The circulation of the water in the sponge cannot, therefore, be a 

 deeply seated action. In very thin slices from the surface of the 

 same species, with the inner portion towards the eye, I have seve- 

 ral times seen the passage of the molecules inward through the 

 in-current pore ; but, notwithstanding this, I have never in that spe- 

 cies succeeded in detecting the cilia ; once only I thought I saw, in 

 one of the cavities immediately within the in -current orifices, the pe- 

 culiar flickering motion which frequently indicates the presence of 

 those organs when their rapid motion precludes all possibility of 

 seeing them ; but I do not attach much value to so slight an amount 

 of evidence of their presence. 



