i8o 



POSITION OF THE EYES 



CHAP. 



Some curious points came out in his table of results. Amalia 

 gagates appears to be surprisingly omnivorous, for out of 197 

 kinds of food it ate all but 25; Avion ater came next, eating all 

 but 40. Liynax arborum, on the other hand, was dainty to a 

 fault, eating only seven kinds of food, and actually refusing 

 Swedes, which every other species took with some avidity. Cer- 

 tain food was rejected by all alike, e.g. London Pride, Dog Rose, 

 Beech and Chestnut leaves, Spruce Fir, Common Rush, Liver- 

 wort, and Lichens ; while all, or nearly all, ate greedily of Pota- 

 toes, Turnips, Swedes, Lettuces, Leeks, Strawberries, Boletus 

 edulis^ and common grasses. Few of our common weeds or 

 hedgerow flowers were altogether rejected. Arion and Limax 

 were decidedly less particular in their food than ITelix, nearly 

 all of them eating earth-worms and puff-balls, which no Helix 

 would touch. Arno^i ater and Limax maximus ate the slime off 

 one another, and portions of skin. Gyclostoma elegans and 

 Hyalinia nitida preferred moist dead leaves to anything else. 



II. Sight 



Position of Eyes. — In the majority of the head-bearing 

 Mollusca the eyes are two in number, and are placed on, or in 

 the immediate neighbourhood of the head. Sometimes they are 

 carried on projecting tentacles or ' ommatophores,' which are 

 either simple (as in Prosobranchiata) or capable of retraction 



Fig. 86. — A, Limnaea peregra Miill. ; e, e, eyes ; t, t, tentacles ; B, Helix nemoralis 

 Miill.; e, e, eyes; t, t, tentacles; p.o, pulmonary orifice. 



like the fingers of a glove (^Helix^ etc.). Sometimes, as in a large 

 number of the marine Gasteropoda, the eyes are at the outer 

 base of the cephalic tentacles, or are mounted on the tentacles 

 themselves, but never at the tip (compare Fig. 60, p. 153 and 



