822 ANIMAL NATURE AS A WHOLE. [iii. 



theless organs of sense, particularly organs of vision; and, 

 since tliese nerves are purely nerves of sensation, these animals 

 must possess a conceptive force /^ But are the organs of the 

 senses in these animals analogous to ours ? Are they — like ours 

 — without ganglia ? Or is it not, that their brain can reflect 

 external impressions in the same way as the ganglia? (624, iv). 

 We see in the senses of taste and touch external senses, the 

 nerves of which are also motor nerves, and accomplish, by 

 their vis nervosa alone, all those movements which they can 

 excite as sentient actions (Haller's ' Physiology/ vol. iv, pp. 615, 

 sqq.). Now, since the organs of the senses in insects and 

 worms are very different from those of animals endowed with 

 mind (15, ii), it is possible that their nerves are altogether 

 motor, like the nerves of touch in sentient animals, and thus 

 they may regulate an animal without there being any sensation. 

 It cannot be maintained, that the organs of the senses are con- 

 stituted for the sole purpose of exciting certain special kinds of 

 external sensations — as the eye for seeing, the ear for hearing, 

 &c. Their proper function is to render the nerves capable of, 

 receiving certain external impressions, which could not be 

 received without the aid of such machinery (55, 42) . If these 

 impressions are felt, the nerves certainly develop a particular 

 kind of external sensation ; but if they act as motor nerves, 

 they excite a particular class of movements only, for they are 

 the same that the sensation caused by the impression would 

 excite (358), and this is their function in animals not endowed 

 with mind. In cases of this kind, the animal would not see 

 with its eyes, nor hear with its ears, nor smell with its nose, 

 but only have the same animal movements excited by the special 

 external impressions, as would result if they were actually felt 

 (542 — 544). The external impression of light in the eye, which 

 sentient animals perceive, and through which they are excited 

 to a thousand volitional movements, can imitate the actions of: 

 the instinct to volitional movements in insentient animals, and 

 excite them directly as nerve-actions (555). Impressions on 

 the ear can excite as nerve-actions the actions of the instincts 

 of self-defence, sexual congress, &c. (559, 560, 566). So also 

 the actions of the instinct for food may be excited in insentient 

 animals as nerve-actions, by external impressions on the nerves 

 of taste and smell (552, 553). 



