SENSES TOUCH. 



183 



will not feel the impression, and evidence its alarm by intel- 

 ligible signs. The intimations which they receive by this 

 medium are probably of a very general character, and have 

 respect only to the motion, the temperature, the hardness 

 or softness, of the impressing body. To judge of the posi- 

 tion, and perhaps in some degree of the form, of bodies, 

 they are provided with special organs, which, when situated 

 on the head, or about the mouth, are denominated tentacula, 

 but when arranged along the sides or on the margins of the 

 cloak, more commonly tentacular filaments. The former 

 are two or four in number, very rarely six,* and in only 

 one or two instances is there a pair, with an odd one behind 

 them : they are of a cylindrical, tapered, or triangular figure, 

 very flexible, and almost always capable of being withdrawn 

 within a sheath or under the collar, at the will of the 

 animal. The filaments are sometimes retractile, and some- 

 times not : many species do not possess them ; but, when 

 they are present, they become the creature's chief ornament. 

 The shell of the Haliotis, for example, if we except the 

 splendid iridescence of its interior, is sufficiently plain and 

 vulgar ; but behold it borne along by the living tenant, its 



Fiat. 32. 



variegated garniture all displayed and vermicular in the 

 smooth and crystal water, and it moves wonder and admi- 

 ration (Fig. 32). The Cypraeae, Trochi, and the family 

 of which the genus Turbo is the type or representative, 

 afford equally fine illustrations, the filaments in some species 



* The Nautilus is remarkable for their unexampled number, surrounding 

 the mouth in successive series, and amounting to little short of a hundred ! 

 They are also retractile within sheaths, and annulated ; but it should he 

 remembered that of this number Jour only seem designed for sensation, and 

 these resemble the tentacula of Doris in their lamellated structure. See 

 Owen's Memoir ; and Cyclop. Anat. and Physiol, i. 526. 



