330 FUNCTIONS OF THE NERVOUS SYSTEM. 



own ganglionic centres, belonging to their respective segments. Now as all these nerves 

 are found' to proceed, in the adult animal from the single pair of Cephalic ganglia, it is 

 obvious that these combine the functions of the ganglionic centres of the nerves of the 

 antenna;, eyes, and palpi, which are all sensory organs, as well as of the maxillary nerves, 

 which must be chiefly motor. And it is equally obvious, that there is nothing in such an 

 animal, which, can be compared to a pair of Cerebral hemispheres; since all the ganglia 

 of the original segments are directly connected with the appendages of those segments 

 respectively. 



427. It is further to be remarked, that the development of the Cephalic 

 ganglia in the Invertebrata always bears an exact proportion to the develop- 

 ment of the eyes ; the other organs of special sense being comparatively 

 undeveloped ; whilst these, in all the higher classes at least, are instruments 

 of great perfection, and evidently connected most intimately with the direc- 

 tion of the movements of the animals. Of this fact we have a remarkable 

 illustration in the history of the metamorphoses of Insects ; the eyes being 

 almost rudimentary, and the Cephalic ganglia comparatively small, in most 

 Larvae; whilst both these organs attain a high development in the Imago, to 

 whose actions the faculty of sight is essential. 



428. Now upon making a similar comparison of the psychical operations 

 of these different classes of animals, we are led to perceive that, as we de- 

 scend from the higher to the lower Vertebrata, we gradually lose the indica- 

 tions of Intelligence and Will, as the sources of the movements of the animal; 

 whilst we see a corresponding predominance of those, which are commonly 

 denominated Instinctive, and which are performed (as it would appear) in 

 immediate respondence to certain sensations, without any intentional adapta- 

 tion of means to ends on the part of the individual, although such adaptive- 

 ness doubtless exists in the actions themselves, being a consequence of the 

 original constitution of the nervous system of each animal performing them. 

 It cannot be doubted by any person who has attentively studied the charac- 

 ters of the lower animals, that many of them possess psychical endowments, 

 corresponding with those which we term the intellectual powers and moral 

 feelings in Man; but in proportion as these are undeveloped, in that propor- 

 tion is the animal under the dominion of those Instinctive impulses, which, 

 so far as its own consciousness is concerned, may be designated as blind and 

 aimless, but which are ordained by the Creator for its protection from danger, 

 and for the supply of its natural wants. The same maybe said of the Human 

 infant, or of the Idiot, in whom the reasoning powers are undeveloped. In- 

 stinctive actions may in general be distinguished from those which are the 

 result of voluntary power guided by reason, chiefly by the two following 

 characters: 1. Although, in many cases, experience is required to give the 

 Will command over the muscles concerned in its operations, no experience 

 or education is required, in order that the different actions, which result from 

 an Instinctive impulse, may follow one another with unerring precision. 2. 

 These actions are always performed by the same species of animal, nearly, 

 if not exactly, in the same manner; presenting no such variation in the means 

 adapted to the object in view, and admitting of no such improvement in the 

 progress of life, or in the succession of ages, as we observe in the habits of 

 individual men, or in the manners and customs of nations, that are adapted to 

 the attainment of any particular ends, by those voluntary efforts which are 

 guided by reason. The fact, too, that these instinctive actions are often seen 

 to be performed under circumstances rendering them nugatory, as reason 

 informs us, for the ends which they are to accomplish (as when the Flesh-fly 

 deposits her egg on the Carrion-plant instead of a piece of meat, or when the 

 Hen sits on a pebble instead of her egg) is an additional proof, that the 

 Instinctive actions of animals are prompted, like the consensual movements 



