GANGLIA OF SPECIAL SENSE : INSTINCTIVE ACTIONS. 381 



the brain in the Invertebrated animals ; and in Fishes they 

 bear a very large proportion to the other parts, their relative 

 size gradually diminishing as we ascend the scale towards 

 Man. JSTow when we study the actions of these lower tribes 

 of animals, we find that those which evidently depend upon 

 sensation, especially the sense of sight, are very far from 

 being of the same spontaneous or voluntary character as those 

 which we perform. We judge of this by their unvarying 

 nature, the different individuals of the same species execut- 

 ing precisely the same movements, when the circumstances 

 are the same, and this evidently without any choice, or 

 intention to fulfil a given purpose, but in direct respondence 

 to an internal impulse. Of this we cannot have a more 

 remarkable example than is to be found in the operations 

 of Bees, "Wasps, and other social Insects ; which construct 

 habitations for themselves upon plans which the most enlight- 

 ened human intelligence could not surpass ; yet which do so 

 without hesitation, confusion, or interruption, the different 

 individuals of a community all labouring effectively for one 

 common purpose, because their impulses are the same (Chap- 

 ter XIV.) 



476. In higher animals we may often notice the effect of 

 similar promptings, by which the various species are guided 

 in their choice of food, in the construction of their habitations, 

 in their migrations, &c. : but these are frequently modified 

 to a certain degree by the intelligence which they possess. 

 The closure of the pupil when the eye is exposed to a strong 

 light, and its dilatation when the light diminishes ( 534), 

 afford a very marked example of this " consensual" class of 

 movements, which differ from the simply-reflex in requiring the 

 stimulus of sensations, but which are, like them, quite indepen- 

 dent both of the reason and of the will. A still more striking 

 illustration, however, is furnished by the mode in which a 

 little Fish, termed the Chcetodon restrains, obtains its food. 

 Its mouth is prolonged into a kind of beak or snout, through 

 which it shoots drops of liquid at insects that may be hover- 

 ing near the surface of the water, and rarely fails in bringing 

 them down. Now, according to the laws of Optics, the insect, 

 being above the water whilst the eye of the fish is beneath, 

 it, is not seen by it in its proper place ; since the rays do not 

 pass from the insect to the fish's eye in a straight line ( 528). 



