20 SEXUAL SELECTION. Part IL 



with the dull-coloured gobies,^^ in which the sexes are 

 not known to differ in colour, and likewise with the 

 sticklebacks (Gasterosteus), in which the males become 

 brilliantly coloured during the spawning-season. The 

 male of the smooth-tailed stickleback (G. leiuriis) per- 

 forms durino- a lono^ time the duties of a nurse with 

 exemplary care and vigilance, and is continually 

 employed in gently leading back the young to the 

 nest when they stray too far. He courageously 

 drives away all enemies, including the females of his 

 own species. It would indeed be no small relief to the 

 male if the female, after depositing her eggs, were 

 immediately devoured by some enemy, for he is forced 

 incessantly to drive her from the nest.^^ 



The males of certain other fishes inhabiting South 

 America and Ceylon, and belonging to two distinct 

 orders, have the extraordinary habit of hatching the 

 eggs laid by the females within their mouths or branchial 

 cavities.^ With the Amazonian species which follow 

 this habit, the males, as I am informed by the kindness 

 of Professor Agassiz, "not only are generally brighter 

 '• than the females, but the difference is greater at 

 " the spawning-season than at any other time." The 

 species of Geophagus act in the same manner ; and in 

 this genus, a conspicuous protuberance becomes deve- 

 loped on the forehead of the males daring the breeding- 

 season. With the various species of Chromids, as Pro- 

 fessor Agassiz likewise informs me, sexual differences 



32 Cuvier, ' Regne Animal,' vol. ii. 1829, p. 242. 



^ See Mr. Warington's most interesting description of the habits of 

 the (-1 aster odr.us leiurus, in ' Annals and Mag. of Nat. Hist.' November, 

 1855. 



^^ Prof. Wyman, in ' Proc. Boston Soc. of Nat. Hist.' Sept. 15, 1857. 

 Also W. Turner, in ' Journal of Anatomy and Phys.' Nov. 1, 1866, 

 p. 78. Dr. Giinther has likewise described other cases. 



