190 MB. C. DAHWI^- OS ITTHHUM S.VITCABTA. 



some of the lower animals males, females, and hermaphrodites 

 of the same species ; we have tlie somewhat more curious case 

 of certain Cirripedos which are hermaphrodites, but are sexually 

 aided by whole clusters of what I have called complemcntal 

 males ; we have, as Mr. Wallace has lately shown, the fp^-ilos of 

 certain Lepidoptera existing under three distinct fon s ; but in 

 none of these cases is there any reason to suspect iu. *' there 

 is more than one female or one male sexual element. With 

 certain insects, as with Ants, in which there exist, besides 

 males and femiales, two or three castes of workers, we have a 

 slightly nearer approach to our case, for the workers are so far 

 sexually affected as to have been rendered sterile. With plants, 

 at least with phanerogamic plants, we have not that wonderful 

 series of successive developmental forms so common with animals ; 

 nor could this bo expected, as plants are fixed to one spot from 

 their birth, and must be adapted throughout life to the same 

 conditions. With plants wc have sexual differences in structure, 

 but apparently less strongly marked than with animals, from 

 causes which are in part intelligible, such as there being no 

 sexual selection ; again, we have that class of dimorphic flowers 

 80 ably discussed recently by Hugo von Mohl, in which some 

 of the flowers are minute, imperfectly developed, and neces- 

 sarily self-fertile, whilst others are perfect and capable of 

 crossing with other flowers of the same species; but in these 

 several cases wo have no reason to suspect that there is more 

 than one female or one male sexual element. When we come to 

 the class of reciprocally dimorphic plants, such as Prvmula, Linum, 

 &c., we first meet with two masculine and two feminine sexes. 

 But these cases, which seemed only a short time since so strange, 

 now sink almost into insignificance before that of the trimorphic 

 species of Lythrmn. 



Naturalists are so much accustomed to behold great diversities 

 of structure associated with the two sexes, that they feel no 

 surprise at the fact ; but differences in sexual nature have been 

 thought to be the very touchstone of specific distinction. We 

 now see that such sexual differences — the greater or less power 

 of fertilizing and being fertilized— may characterize and keep 

 separate the coexisting individuals of the same species, in the 

 same manner as they characterize and have kept separate those 

 groups of individuals, produced from common parents during the 

 lapse of ages or in different regions, which we rank and deno- 

 minate as distinct species. 



