454 Report of the State Geologist. 



the tentacles consists mainly of water obtained from without, 

 there can, I think, be little doubt ; and yet I have in vain sought 

 for any opening through which the external fluid can gain 

 admittance into the interior. I have allowed the transparent 

 genera Cristatella and Lophopus to remain many hours in car- 

 mine without being able to detect a single particle of this pig- 

 ment in the perigastric space, though I have seen this space 

 rapidly empty itself on the removal of the animal from the 

 water and again fill on restoring it to its natural element. Yon 

 Beneden believed that he had detected in Alcy< )nella, apertures, 

 which he named 'bouches aquiferes,' at the base of the ten- 

 tacles ; but this distinguished naturalist is certainly here in error, 

 a^s indeed he himself subsequently admits." Meten asserts that 

 an opening exists in the vicinity of the anus, through which he 

 himself had witnessed the escape of the egg of Alcyonella, and 

 SiEBOLD corroborates him. But, without doubt, any such aper- 

 ture was the result of a rupture. One objection to the theory 

 that the water finds its way through tubes in the cell walls too 

 minute to be detected is that in many forms the cell tubes are 

 so closely packed together that no water has access to the 

 exterior of the cell walls. 



The perigastric fluid enters the tentacles through the lopho- 

 phore, and thus becomes aerated by the constant flow of the 

 oxygenating medium over their surface by the action of the 

 vibratile cilia, though if the perigastric cavity can be emptied 

 and filled as quickly as stated by Allman, any special aeration by 

 the tentacles would seem unnecessary. While the aeration of the 

 blood or perigastric fluid can be easily understood when the animal 

 is protruded, it is difficult to understand how the oxygenation 

 can be effected when the animal is withdrawn in the cell, for 

 then the orifice is completely closed by the folding of the sides of 

 the orifice, and there is no communication with . the exterior. 

 The only explanation can be that, as is the case with bivalves, a 

 constant aeration of the blood from the air in the water is 

 unnecessary. 



There can be little doubt that the perigastric fluid is nutritive, 

 and holds in suspension the results of digestion, which proba- 

 bly exude through the walls of the stomach. It is only on such 

 a supposition that we can understand the nourishment of the 



