4 LIMNEA. 



for the present. We know of no American 

 species. 



Dr. Sharpey suggests that the broad tenta- 

 cles in the genus Limnea may be instrumental 

 in aquatic respiration, as they are provided with 

 cilia;* these, however, are not found upon the 

 tentacles alone, as I have observed them upon 

 the edges of the mantle and foot, and even 

 upon the sole of the latter; moreover, they are 

 not confined to the Limneans; the mantle and 

 foot (but not the tentacles) of Melania, being 

 similarly supplied. I had thought that the long 

 and slender tentacles of Physa might be, in 

 part, organs of scent;t and that the ciliary 

 currents are necessary to make them acquaint- 

 ed with the locality of their food, the aroma of 

 which could not well spread through the quiet 

 waters they inhabit — but the genus Amnicola, 

 which does not generally inhabit stagnant 

 waters, has slender ciliated tentacles also.J 



* Cyclopaedia of Anat., art. Cilia, vol. i. p. 621. 



j- Cuvier, Regne Animal Moll., p. 46. 



\ In discussing this question, it should be borne in mind, that 

 the oxygenation of the system through the external surface, has 

 been effected in frogs, which have been confined under water for 

 the purpose of making the experiment. In this case, however, 

 the water may find its way to the lungs. 



