JOURNAL OF CONCHOLOGY. 305 



ON THE ORGANS OF SENSE IN THE 

 BRITISH LAND AND FRESHWATER MOLLUSCA. 



By ROBERT SCHARFF, Ph.D., B.Sc, &c. 



[Read before the Conchological Society.] 



In the following paper on the sensory organs of our Land and 

 Freshwater Shells I propose to take up the organ of sight first. 

 Although there are well developed organs of touch, which may 

 in some cases be distributed all over the surface of the body, 

 I intend to deal here merely with the senses of Sight, Hearing, 

 and Smell. I may also state that I am not giving any results 

 of original investigation, but only a succint resume or rather a 

 compilation of what has recently been published on this subject, 

 without too deeply going into histological details. Only com- 

 paratively few land and freshwater shells have been examined 

 as to the structure of their sensory organs, but from what has 

 been done we may safely assume that the differences in the 

 organization of the various genera are only very slight, and I 

 shall refer to them as we go on. 



The Organs of Sight. 



The eye is present in all land and freshwater gasteropods, 

 while it appears to be completely wanting in our Lamellibranchs. 

 In some of the marine bivalves, on the other hand, such as 

 Pecten, Cardium, and Spondylus, we find well-developed organs 

 of sight. Thus we have to deal here simply with the eyes of 

 the Gasteropoda. 



The eyes always lie in duplicate number on the head, 

 mostly on the top of the two great tentacles, for example, in 

 many land shells, but in many cases at their outer base, as in 

 Cyclostoma. In the freshwater Pulmonates, for instance in 

 Limnsea, they lie at the inner, and in Bythinia at the outer base 

 of the two tentacles. In all snails having four tentacles the 

 eyes are situated at the apex of the two larger ones (except 



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