526 RELATION OF INSTINCTIVE TO INTELLIGENT!AL 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 hear 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 
Yertebrata, 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 Keflex 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 
