66 OBSERVATIONS ON NAIADES, 



was very evident. At first the slightest agitation or movement of the 

 vessel caused them to close their valves instantly. Being almost daily 

 disturbed, this alarm after a time ceased, particularly with my fine 

 cariosus, which now suffered even the agitation of the water without 

 closing the valves, stretching out its fine dark and beautiful tentacula 

 from the borders of its mantle, and forming by the contact of its edges 

 two openings one below the other. 



From the superior of these openings the constant stream ejected could 

 be plainly perceived for two inches elevating the water at its surface. 

 Being very anxious to ascertain through what part the water necessary 

 to supply this stream was carried into the shell, I discovered it, after 

 many experiments, to pass in by the inferior opening ; that it passed 

 out by the superior one had always been evident. This operation 

 was unremitted while the water was fresh ; when left unchanged for 

 some days this current invariably ceased. Doubting the correctness of 

 my former idea, as to the probability of' their feeding on animalcula. 

 from the circumstance of finding the passage of the water to exist only 

 while fresh, and never when animalcula were visible even with a 

 microscope of great power, I instituted some experiments by passing 

 pieces of bread, very small pieces of worms, &c. between the tentacula. 

 Several of them would sometimes remain for some minutes within 

 the mantle and so far within as to be invisible, but they were in every 

 case in a very short time thrown out with a rapid and sudden jet of 

 water to the opposite side of the vessel. 



These experiments were frequently repeated during the course of a 

 year upon the same specimen, and the result was uniformly the same. 

 No food introduced into the shell could be ascertained to have remained ; 

 it may therefore be pretty safely concluded, that neither animalcula 

 nor food in a more solid state are necessary to the nourishment of the 

 Naiades. What then are we to conclude it to be ? Would the decom- 

 position of water serve the purpose of nourishment as well as breath- 

 ing ? Certain it is, that during the many years I have been in the habit 

 of almost constantly having them alive for examination, dissection, &c. 

 I have never in any instance given them food, unless it was conveyed 

 invisibly to them in the pure water with which our city is supplied 

 through our works from the river, and which was given them every 

 few days. 



