318 ANIMAL NATURE AS A WHOLE. [iii. 



required for the life and preservation of an animal organism, can 

 be effected by the vis nervosa only; nay, even the greater num- 

 ber of the actions of sensational conceptions, desires, instincts, 

 &c., may be induced by it, simply as nerve-actions ; secondly, 

 because experiments on decapitated animals prove it. 



624. As to a large class of animals, it has never been proved 

 that they are endowed with animal-sentient forces, and it is 

 highly improbable that they are : 



i. Because we can detect no traces of mind or a conceptive 

 force with which their animal forces can co-operate (6). If 

 those movements of sensation and volition, which occur in de- 

 capitated animals, as results of the vis nervosa solely, are all 

 that can be adduced as proofs of the existence of an external 

 sensation, then an oyster, a sea- worm, a snail, a polype, do not 

 manifest, during their whole existence, a single movement 

 which renders the existence of conceptive force in them at all 

 probable. 



ii. Because many animals, unlike those undoubtedly sentient, 

 have not a head distinct from the body (15, ii). We may con- 

 clude from analogy, with some probability, that since all animals 

 to which we can undoubtedly attribute the possession of a con- 

 ceptive force and consciousness, have heads distinct from the 

 body, it follows that the former must be governed by forces alto- 

 gether different from the latter ; and since these are regulated 

 by animal-sentient forces, the others must be governed by the 

 vis nervosa, for there is no other force (356). The relations of 

 mental endowments to the cerebral development is specially 

 noticed by Haller. ('Physiology,' vol. iv, p. 634<.) 



iii. Because, although all animals possess the analogues of 

 nerves, the most numerous genera have nothing analogous to a 

 brain, even when they have a head distinct from the body; or, 

 indeed, a part which in movements all others are accustomed to 

 follow. This principle is of very great importance. In those 

 animals undoubtedly endowed with sensation, there is a distinct, 

 complete brain, the seat of mind (10) : all observations establish 

 this doctrine — none are opposed to it — none render it even 

 doubtful. Yet this undoubted dwelling-place of the soul is not 

 a necessary portion of many animals; nor necessary to the per- 

 formance of numerous acts, performed in virtue of the vis 

 nervosa, by animals after decapitation, in the same order, with 



