296 On the Sense of Feeling. 



been thrown by M. Elirenberg, seem to possess an integument, and ])ro- 

 bably enjoy the sense of tact ; — sensibility to heat they certainly possess. 



The actiniae and certain zoophytes, as the euryale and family of crinoidea, 

 possess teutacula of considerable length, with which they apprehend their 

 food, and which, if endowed with sensibility, may certainly convey to them 

 very accurate ideas concerning the forms of bodies. 



The starfish and sea urchin, radiated echinoderraata, possess a very ob- 

 vious integument ; and as in these radiated animals the nervous system 

 begins to be exhibited, we may naturally expect to find the organs depend- 

 ing upon it developed in like proportion. 



In the starfish the integument is sometimes soft and smooth, but most 

 usually scabrous and tnberculated ; the covering being fibrous, and calca- 

 reous granules occupying the interstices of the fibres. 



The investing membrane of the echini is thin and almost gelatinous, but 

 in its interstices are deposited the calcareous particles for which these 

 animals are remarkable. The deposition of this calcareous case does not 

 resemble that of a regular shell ; the particles would rather seem to be 

 deposited in a chrystalline form, a fact which has been supposed to ac- 

 count for the peculiar arrangement of the chrystals, in such of these cases 

 as are found fossil. The spines of this animal seem intended only for 

 passive defence aud locomotion. 



Jn the insects we shall find a prodigious improvement in the organs of 

 the senses. 



Insects are encased in a calcareous or horny envelope, presenting by far 

 the most complete form of an external skeleton, and formed, according to 

 Latreille, by the excretion between the cutis and cuticle, upon what has 

 been termed the mucous tissue. It is in this tissue that the brilliant co- 

 lours of insects reside. 



Among insects the sense of tact varies remarkably, according to the 

 condition in which they happen to exist for the time ; their external surface, 

 upon which the sense, of course, resides, being subject to great modifica- 

 tions, from the larval state in which it is soft and pulpy, to the perfect sheath 

 of the beetles and other coleoptera, in whom it is hard and horny. 



In insects, the organs of touch, of prehension, and of locomotion, are 

 found to be more or less distinct : the latter, though well calculated from 

 their mobility and joint'jd structure to be applied to the surfaces of bodies, 

 being supposed to be superseded, as organs of touch, by the more delicate 

 palpi placed near the mouth. 



It is probable, however, and supposed by most entomologists, that the 

 antennce, ov feelers, as they have been termed, are also organs of touch to 

 most of the insect tribes : this opinion has arisen from their universality, 

 their flexibility, their incessant motion when the animal walks, and the 

 constant employment of them in examining the surface of bodies presented 

 to it. 



