58 THE USE AND NATURE 



an organism, in one of the simple animals to which we 

 are referring, may be more or less impressible to shocks or 

 impacts from contact with surrounding bodies, it often 

 happens that such impressions more frequently fall upon, 

 and are more readily received by, certain appendages 

 situated at the anterior extremity of the animal, in close 

 proximity to the mouth. These specialized parts, or 

 * tactile appendages', are known as papillae, setae, tentacles, 

 antennae, or palpi, according to the forms which they 

 assume in different animals. 



Why such organs should be developed so frequently at 

 the anterior extremity of the animal, and in the neigh- 

 bourhood of the mouth rather than on other parts of the 

 body, is not difficult to explain. Whatever the mode by 

 which they are called into being (and the most opposite 

 views are entertained upon this subject), it seems obvious 

 that, if organs of this nature are to be present at all, 

 they should be found in situations where they may be 

 put to most use. In an animal accustomed to active 

 locomotions, the mouth is, with only a very few excep- 

 tions, situated on the part of the body which is habitu- 

 ally directed forward. And of the diverse objects coming 

 into contact with it, some are of a nature to serve as food, 

 and some are not. A high degree of impressibility natu- 

 rally becomes developed, therefore, in this situation, 

 where the parts are exercised so largely with impressions 

 connected with the discrimination and capture of food. 

 These organs are, in fact, not unfrequently both tactile 

 and prehensile — this combination being more especially 

 met with in sedentary forms of life, like the Hydra, the 

 Sea-anemone, or some of the tentaculated Worms. 



Taste. — But it often happens that the solid bodies 

 serving as food are more or less readily soluble, so that in 

 animal organisms comparatively low in the scale of com- 



