SPECIALISATION OF FUNCTION. 1 i. 



relation with the organism, and the organism in turn reacts 

 upon the external world. 



Of these three, the functions of nutrition and reproduction 

 are often collectively called the functions of organic or vege- 

 tative life, as being common to animals and plants ; while the 

 functions of correlation are called the animal functions, as 

 being more especially characteristic of, though not peculiar 

 to, animals. 



6. DIFFERENCES BETWEEN DIFFERENT ANIMALS. 



All the innumerable differences which subsist between dif- 

 ferent animals may be classed under two heads, corresponding 

 to the two aspects of every living being, morphological and 

 physiological. One animal differs from another either mor- 

 phologically, in the fundamental points of its structure, 

 or pltysiologically, in the manner in which the vital func- 

 tions of the organism are discharged. These constitute the 

 only modes in which any one animal can differ from any 

 other ; and they may be considered respectively under the 

 heads of Specialisation of Function and Morphological type. 



a. Specialisation of Function. All animals alike, whatever 

 their structure may be, perform the three great physiological 

 functions ; that is to say, they all nourish themselves, re- 

 produce their like, and have certain relations with the ex- 

 ternal world. They differ from one another physiologically 

 in the manner in which these functions are performed. Indeed, 

 it is only in the functions of correlation that it is possible 

 that there should be any difference in the amount or perfection 

 of the function performed by the organism, since nutrition and 

 reproduction, as far as their results are concerned, are essentially 

 the same in all animals. In the manner, however, in which 

 the same results are brought about great differences are ob- 

 servable in different animals. The nutrition of such a simple 

 organism as the Amoeba is, indeed, performed perfectly, as far 

 as the result-to the animal itself is concerned as perfectly as 

 in the case of the highest animal but it is performed with 

 the simplest possible apparatus. It may, in fact, be said to be 

 performed without any special apparatus, since any part of 

 the surface of the body may be extemporised into a mouth, 

 and there is no differentiated alimentary cavity. And not 

 only is the nutritive apparatus of the simplest character, but 

 the function itself is equally simple, and is entirely divested of 

 those complexities and separations into secondary functions 

 which characterise the process in the higher animals. It is 

 the same, too, with the functions of reproduction and correla- 

 tion ; but this point will be more clearly brought out, if we 



