SENSATION. 87 



auditory orojans occur among different members of the group 

 in widely different parts of the body. Thus in tlie lobster 

 and cray-fish they are situated in the head at the base of the 

 antennules, while in some of the crabs {e.g., Mysis) they occur 

 in the tail. Among the Orthoptera, again, they are found in 

 the tibit^ of the front legs, or, in other species, upon the sides 

 of the thorax. In other insects, probability points to the 

 organs of hearing being placed in the antennae. These facts 

 prove that in the Articulata the sundry kinds of auditory 

 organs must have arisen independently, and have not been \P 

 inherited from a common ancestor of the group ; and it is 

 remarkable that this should have been the case even within 

 the limits of so comparatively small a subdivision as that 

 which separates a crab from a crayfish or a lobster."^ 



There can be no question that the sense of smell is well • 

 developed in at least many of the Articulata, although, save 

 in a few cases, we are not yet in a position to determine the 

 olfactory organs. Thus the account which I quoted in 

 '' Animal Intelligence" (p. 24), from Sir E. Tennent, concern- 

 ing the habits of the land leeches of Ceylon, proves that 

 these animals must be accredited with a positively astonishing 

 delicacy of olfactory perception, seeing that they smell the 

 approach of a horse or a man at a long distance. In earth- 

 worms the sense of smell is feeble, and seems to be confined 

 to certain odours.-f- Sir John Lubbock has proved by direct 

 experiment that ants are able to perceive odours, and that 

 they appear to do so by means of their antennse. The same ' 

 remark applies to bees, and the general fact that many insects 

 can smell is shown by the general fact that so many species 

 of flowering plants, which depend for their fertilization upon 

 the visits of insects, give out odours to attract them. That 

 the Crustacea are able to smell is rendered evident by the 

 rapidity with which they find food. I have recently been 

 able to localize the olfactory organs of crabs and lobsters by 

 a series of experiments which I have not yet published, and 

 which would occupy too much space here to detail. I shall 

 therefore merely say that they are situated in the pair of 

 small antennules, the ends of which are curiously modified in 

 order to perform the olfactory function. That is to say, the 



* Analogous facts are to be observed in the case of the Eye among 

 Yermes, and also, as we shall presently see, among Moliusca. 

 f Darwin, loc. cit.^ p- 30. 



