GENERAL IDEAS. 585 



affinities, does not proceed from characters, but from the idea expressed 

 in each group, and forms from these, according to the laws of thought, 

 a philosophical structure. It is requisite, as well for the discovery of 

 the conception and its formation into an idea, as for the constructing of 

 the system, to be thoroughly acquainted with all forms, both in their 

 external and internal characters, for it is these which express the con- 

 cealed idea : when these ideas are found, their arrangement offers of 

 itself, if we but keep in view the object of the natural system, namely, 

 the discovery of analogies and affinities. This concealed idea is properly 

 the true character, and which is expressed in a natural group, and 

 so distinguishes it ; if we have the idea, the character is conveyed 

 with it. These ideas are expressed in the history of the development, 

 or in the manner in which the individual has evolved itself from its 

 origin ; then in the form and composition of the internal organs ; then 

 in the figure, structure, and number of its external organs ; and, lastly, 

 in its functions, both external, and more particularly those of the 

 internal organs. Where there is a resemblance or similarity in all 

 these relations, there is found a perfect affinity ; but where only some 

 resemble and others differ, there it is only partial, and it is the greater 

 the more and more perfectly the several determinate causes harmonise 

 together. We hence distinguish several kinds of affinity, namely, the 

 following * : 



C3 



1. Gradational affinity. This is founded upon the resemblance of 

 the several organs in the grades of development, for example, upon a 

 conformity in the development of the organs of the mouth, whether 

 these are manelibulate or haustellate ; upon a conformity in the me- 

 tamorphoses, &c. Insects which present these resemblances in their 

 organs, and the development of these organs, are brought together 

 in the same group. 



2. Parallel affinity. This is expressed in the mutual relation of the 

 developed forms of individual organs to the rest. It may happen that 

 whilst the remaining organs have acquired a tolerably equal develop- 

 ment, one passes through several, either higher or lower, forms of 

 development. Thus are produced : 



a. Changes of external form in the same grades of organisation, for 

 instance, beetles with elongate proboscideal mouths imitate the mouths 



* See Schulz natiirliches System der Pflanzenreiches. Berlin, 1H32. flvo. p. 13'2, &c. 



