Jhap. II.] INDIVIDUAL DIFFERENCES. 55 



.^lorphie in other countries, and likewise, judging from 

 Brachiopod shells, at former periods of time. These 

 facts are very perplexing, for they seem to show that 

 this kind of variability is independent of the conditions 

 of life. I am inclined to suspect that we see, at least 

 in some of these polymorphic genera, variations which 

 are of no service or disservice to the species, and which 

 consequently have not been seized on and rendered 

 definite by natural selection, as hereafter to he ex- 

 plained. 



Individuals of the same species often present, as is 

 known to every one, great differences of structure, in- 

 dependently of variation, as in the two sexes of various 

 animals, in the two or three castes of sterile females 

 or workers amongst insects, and in the immature and 

 Larval sta|tes of many of the lower animals. There 

 are, also, j cases of dimorphism and trimorphism, both 

 ''Fith aniihals and plants. Thus, Mr. Wallace, who 

 fi'ls lately called attention to the subject, has shown 

 ''''i^'at the females of certain species of butterflies, in the 

 i^-iialayan archipelago, regularly appear under two or 

 '^'^'pn three conspicuously distinct forms, not connected 

 '^y*, intermediate varieties. Fritz Miiller has described 

 but more extraordinary cases with the males 

 Brazilian Crustaceans: thus, the male of a 

 Tanajs regularly occurs under two distinct forms; one 

 of thgge :tias strong and differently shaped pincers, 

 ^^^ the ot !ier has antennas much more abundantly f ur- 

 nisheq ^jy^ smelling-hairs. Although in most of these 

 cases, the two or three forms, both with animals and 

 plants,^ are! not now connected by intermediate gra- 

 dations, it IS. probable that they were once thus con- 

 nefited. Mr. Wallace, for instance, describes a certain 

 6 



anaJiogous 

 of e)ertain 



