234 HABIT AND INTELLIGENCE. [cHAP. 



the leaves and flowers should be combined in the same 

 Their cor- way. The resemblance between the form of the com- 

 relations pound leaf and of the umbel has, I believe, nothincr to do 



not due ^ ' ' a 



to adapta- with their functions, and is comparable rather to those 

 ^°°^' laws of symmetry that govern crystalline form. 



The resemblance, or difference, between flowers of op- 

 posite sexes is, of course, of exactly the same kind as the 

 resemblance or difference between flowers and leaf-bearing 

 axes. Both the sets of flowers consist of modified leaves ; so 

 that, however different they may be, the difference cannot be 

 Differences fundamental. The difference between the sexes among all 

 sexes'^not Organisms that have the sexes on distinct individuals 

 funda- appears to be of this kind. It is often very considerable 

 and most conspicuous, but never really fundamental. In- 

 deed, it is a remarkable fact that the secondary sexual 

 characters of any species are generally very variable as 

 Secondary between individuals of the species.^ By secondary sexual 

 characters characters are meant those sexual characters which do not 

 are va- belong to the sexual organs. I believe it may be added 

 that such characters usually appear comparatively late in 

 life. Thus, among the true insects, important as are the 

 wings for the purposes of their life, their presence or 

 absence is not a fundamental character, as is shown by 

 these three criteria, that they are never developed till long 

 after the insect has left the egg ; that they are sometimes 

 present and sometimes absent in the same species ;2 and 

 that they are frequently a sexual character, being found on 

 the males only. 



This general law, that the differences between the two 



sexes of the same species are not such as to affect the 



fimdamental characters, is what might have been expected, 



Metamor- and it needs no special explanation. The same may be 



phosis, gg^-(j q£ ^Yie general law of metamorphosis, which is, that 



the larva is formed on the same general type as the 



perfect form, but is of a lower grade of organization. The 



in insects, true insects are the highest of aU articulated animals, and 



the larvae of those insects which undergo much metamor- 



'&"- 



1 Darwin's Origin of Species, p. 184. 

 * This is the case among some beetles. 



