526 RELATION OF INSTINCTIVE TO INTELLIGENTIAL ACTIONS. 



wonderful in the Invertebrata, which possess the least Intel- 

 ligence ; and, on the contrary, they are fewest and least 

 remarkable in Man, whose Intelligence is highest. From 

 the constant proportion they bear to the size of the ganglia 

 of sensation, which form nearly the whole nervous mass in 

 the head of Insects, &c., and a large part of that of the lower 

 Vertebrata, but which are comparatively small in the Mam- 

 malia and especially so in Man, there seems good reason to 

 regard these organs as their chief instruments. III. The 

 third and highest class of actions, is that in which Intelligence 

 is the guide, and the Will the immediate agent. The animal 

 receives sensations, forms a notion of their cause, reasons 

 upon the ideas thus excited, perceives the end to be attained, 

 chooses or devises the means of accomplishing it, and volun- 

 tarily puts those means into execution. These actions are 

 seen, in their highest and most complete form, in Man ; but 

 they are not confined to him ; for, as will be shown hereafter, 

 true reasoning processes are performed by many of the lower 

 animals. There can be no doubt that the Cerebral Hemi- 

 spheres, which form the Brain properly so called, constitute 

 the instrument by which these actions are executed; for 

 we find that their size and development bear a very regular 

 proportion to the degree of Intelligence which the animal 

 possesses. 



693. It follows, then, that the lower we descend in the 

 scale of Animal life, the larger is the proportion of the move- 

 ments of any particular species which we are to attribute to 

 the Reflex and the Instinctive classes ; whilst the proportion 

 which is due to Intelligence and Will diminishes in a like 

 degree. Thus we have seen that the ordinary movements of 

 locomotion, which Man performs in the first instance by volun- 

 tary effort, are reflex in Insects ( 445) and there can be no 

 reasonable doubt that the movements of the tentacula of the 

 Hydra, by which it entraps its prey and draws it to the entrance 

 of its stomach ( 121), are of a reflex, rather than a voluntary 

 or instinctive character, since they are obviously analogous to 

 those movements of the pharyngeal muscles, by which the food 

 is grasped and carried into the alimentary tube of the highest 

 animals ( 195). There is one curious fact, which would 

 seem to indicate a difference between them, but which is 

 really a strong argument in favour of their analogy. It is 



