•If] Dr. Johnston on Scottish MoUusca. 



plicity of plan, it is probable that the ins tincta and sensibilities 

 of these mollusca are few and of a low character*; 



animal sine fraudc, dolisque, 



Innocuum, simplex, 



and we know no trait in their habits that is repugnant to this 

 inference. Cuvier says he could detect no evidence for the 

 existence of more senses than sight and touch : the former is 

 seated in the small black specks which may be seen, in some 

 of the genera, at the bases of the tentacula ; the latter sense 

 has no particular locality, but is diffused over the whole sur- 

 face, though exercised more especially, and with greatest de- 

 licacy, by means of the endermoid processes, such as the ten- 

 tacula and branchial fringes. I cannot, however, but suspect 

 that the tentacula have some more specific use ; for their struc- 

 ture, in Doris and Tritonia at least, is complex, and their po- 

 sition ill suited to organs intended to be employed as tactors. 

 Blainville supposes, with some show of reason, that they may 

 be organs of smell f; and, we may add, perhaps of hearing also. 

 " The slow-moving molluscous animals," says Professor Grant, 

 " are less provided with organs for perceiving the properties 

 of outward bodies than the active articulated classes ; but many 

 of the higher*^:>ulmonated gasterops seem both to hear and to 

 smell, although the precise seats of these feelings have not 

 been determined, and Tritonia arborescens emits audible sounds 

 under water, which are, without doubt, intended to be heard 

 by others of the same species, as we see in insects, and pro- 

 bably to serve as a means of communication between these 

 hermaphrodite and almost blind animals, although the organs 

 have not been detected which are appropriated to their per- 

 ception J". 



Some foreign species are rapid in their movements, swim- 

 ming with ease in the ocean and on its surface, but the pro- 



* Lamarck, Anim. s. Vert. vi. i. 265. 



t " Enfin une autre opinion qui est la notre, e'est que e'est l'extremite 

 des tentacules veritables, ou de la premiere paire d'appendices qui est l'or- 

 gane d'olfaction. La peau y est en effet encore plus molle, plus lisse, plus 

 delicate que dans aucun autre endroit, et le nerf qui s'y rend est plus con- 

 siderable." — Man. de Malacologie, 107. Carus's objection to this opi- 

 nion appears to be founded on a verbal quibble. — See Camp. Anat. i. 73. 

 Trans. 



X Outlines of Comp. Anat. 279. 



