48 THE FUNCTIONS OF LIFE. 



be attained is dependent upon certain definite conditions, ex- 

 cluding the possibility of modification, that these conditions 

 are uniformly and strictly adhered to. But wherever that 

 absolute necessity does not exist, and there is afibrded scope 

 for deviation, there we are certain to find introduced all 

 those modifications which the occasion admits of. Not only 

 is this tendency to variety exemplified in the general ap- 

 pearance and form of the body, but it also prevails in each 

 individual organ, however minute and insignificant that or- 

 gan may seem. Even when the purpose to be answered 

 is identical, the means that are employed are infinitely di- 

 versified in different instances, as if a design had existed of 

 displaying to the astonished eyes of mortals the unbounded 

 resources of creative power. While the elements of struc- 

 ture are the same, there is presented to us in succession 

 every possible combination of organs, as if it had been the 

 object to exhaust all the admissible permutations in the order 

 of their union. 



Some wise purpose, though dimly perceptible to our im- 

 perfect understandings, is no doubt answered by this great 

 law of organic formation, the law of variety. That it is not 

 blindly or indiscriminately followed, is apparent from its 

 being circumscribed within certain limits, and controlled by 

 another law, w^hich we have next to consider — that of con- 

 formity to a definite type. 



The most superficial survey of nature is sufficient to show 

 that there prevail certain general resemblances among great 

 multitudes of species, which lead us to class them into more 

 or less comprehensive groups. Thus in the animal kingdom, 

 quadrupeds, birds, fishes, reptiles, shell-fish, and insects, 

 compose natural assemblages or classes, and each of these 

 is readily divisible into subordinate groups or families. Now 

 it results from a closer examination of the structure and 

 economy of plants and animals, that the formation of all the 

 individual species comprehended in the same class, has been 

 conducted in conformity with a certain ideal model, or type, 

 as it is called. Of this general type all the existing forms 

 appear as so many separate copies, differing, indeed, as to 



