114 Oh Unity of Function in Organized Beings, 



same author) " that the objects of the existence of animals re- 

 quire that the mental actions of the nervous system should exert 

 a powerful controlling influence over all the textures and organs 

 composing an animal." 



The organs of sensation, when examined in the ascending 

 scale of animals, will, I think, afford us illustrations of the same 

 general principles. We may perceive that the special functions 

 of sight, hearing, and smell, are rather elaborated out of the ge- 

 neral sense of touch than superadded to it ; and there would not 

 therefore appear, a priori, any physiological impossibility in the 

 fifth pair supplying'a certain power of sight when the optic nerve 

 is absent, as in the mole ; and, if the phenomena of the trans- 

 ference of sensation should ever be indisputably established, 

 their explanation on the same pi'inciples will be easy. 



Without entering into any detail with regard to the structure 

 of the various organs of locomotion in animals, it is easy to ob- 

 serve the intimate connection which exists in the lower classes of 

 this kingdom between the exercise of this function, and those 

 movements which are essential to the maintenance of the organic 

 life. Thus the cilia, which in so many of the aquatic tribes are 

 almost the sole instruments of progression, serve also to bring 

 supplies of food to the mouth, and of water to the respiratory 

 organs. In the higher classes we see each of these functions per- 

 formed by a special apparatus, but still a connection may be 

 traced ; and I know not a more striking illustration of it than 

 the structure of the locomotive system of birds. In this class, 

 as in insects, a high amount of respiration has to be combined 

 ■with general buoyancy of the body ; and this object is attained 

 by the general diffusion of the respiratory oi-gans. But in in- 

 sects, the principal organs of progression are merely an extension 

 of the respiratory system ; whilst in birds, a special locomotive 

 apparatus is evolved, which still, however, retains a certain con- 

 nection with the function of respiration. 



