CHAPTER VI. 



POLYMORPHISM. 



" Ce penple de Pygmees, de Troglodytes, est, en effet, digne de toute noire 

 admiration. Peut-on voir'une societe dont les membres qui la composent aient 

 plus d'amour public? qui soient plus desinteresses? qui aient pour la travail 

 nne ardour plus opiniatre et plus soutenue? Quel singulier phenomene ! Je ne 

 vois dans la tres-grande majorite de ce peuple que des etres sonrds a la voix 

 de 1'amonr, incapables meme de se reproduire, et qui goutent neanmoins le senti- 

 ment le plus exquis de la maternite, qui en ont toute la tendresse, qui ne 

 pensent, n'agissent, ne vivent en un mot que pour des pupilles dont la Nature 

 les lit tuteurs et nourriciers. Cette republique n'est pas sujette a ces vicissitudes 

 de formes, a cette mobilite dans les pouvoirs, a ces fluctuations perpetuelles 

 qui agitent nos republiques, et font le tourment des citoyens. Depuis que la 

 fourmi est fourmi, elle a toujours vecu de meme; elle n'a eu qu'une seule 

 volonte, qu'une seule loi, et cette volonte, cette loi ont constamment pour base 

 I'amour de ses semblables." Latreille, " Histoire Naturelle des Fourmis," 1802. 



There is a sense in which the term polymorphism is applicable to 

 all living organisms, since no two of these are ever exactly alike. But 

 when employed in this sense, the term is merely a synonym of " varia- 

 tion," which is the more apt, since polymorphism has an essentially 

 morphological tinge, whereas variation embraces also the psychological, 

 physiological and ethological differences between organisms. In 

 zoology the term polymorphism is progressively restricted, first, to 

 cases in which individuals of the same species may be recognized as 

 constituting two or more groups, or castes, each of which has its own 

 definite characters or complexion. Second, the term is applied only 

 to animals in which these intraspecific groups coexist in space and do 

 not arise through metamorphosis or constitute successive generations. 

 Cases of the latter description are referred to " alternation of genera- 

 tions " and " seasonal polymorphism." And third, the intraspecific 

 groups of reproductive individuals existing in all gonochoristic, or 

 separate-sexed Metazoa are placed in the category of " sex " or 

 "sexual dimorphism." There remain, therefore, as properly represent- 

 ing the phenomena of polymorphism only those animals in which 

 characteristic intraspecific and intrasexual groups of individuals may 

 be recognized, or, in simpler language, those species in which one 

 or both of the sexes appear under two or more distinct forms. 



As thus restricted polymorphism is of rare occurrence in the animal 

 kingdom and may be said to occur only in colonial or social species 

 where its existence is commonly attributed to a physiological division 



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