22 TASTE-ORGANS OF THE LOWER ANIMALS. 



It will be observed that these structures give us no 

 help to realize in what actually consists the sense of 

 taste. We know that we possess it ourselves. We 

 perceive that other animals can select, and appear to 

 enjoy, their food, and hence we ascribe to them a 

 similar faculty. We know that in our own case this 

 sense resides in the mouth, and we assume that it 

 must do so in other animals; we find in the mouth 

 certain structures, and we infer that to them is due 

 the sensation of taste. Even in our own case the 

 inferences are, perhaps, not very clear, and certainly the 

 facts, as yet known, aid us but little in framing any 

 definite idea of the process. 



But if our knowledge is so imperfect in the case of 

 the higher animals, it becomes much more so in the 

 lower groups. 



In the Mollusca, Annelida, and lower groups, we know 

 scarcely anything of the organ of taste, though we 



can hardly doubt that such 

 exists. 



Medusae (jelly-fishes) are 

 very sensitive to any change 

 in the composition of the sea- 

 w^ater ; for instance, they sink 

 below as soon as it begins to 

 rain. It is difficult, however, 

 to say which sense is affected. 

 In Asterope (a marine worm 

 belonging to the Alciopidse), 

 Greef has described, in the 

 skin of the proboscis, certain 

 peculiar club-shaped, ringed bodies, which taper into a 

 thread connected with a nucleated cell. These he 



Fig. 24.— Inner layer of the skin 

 of the proboscis of Asterope Can- 

 dida, X 400 rafter Greef). a. 

 Cuticle; h, terminal (nerve) 

 organs; c, ganglionic cells; d, 

 longitudinal muscle ; e, trans- 

 verse muscle. 



