20 SEXUAL SELECTION. [Part II. 



Prof. Agassiz, " not only are generally brighter than the 

 females, but the difference is greater at the spawning-sea- 

 son than at any other time." The species of Geophagus 

 act in the same manner ; and in this genus, a conspicuous 

 protuberance becomes developed on the forehead of the 

 males during the breeding-season. With the various spe- 

 cies of Chromids, as Prof. Agassiz likewise informs me, 

 sexual differences in color may be observed, " whether 

 they lay their eggs in the water among aquatic plants, or 

 deposit them in holes, leaving them to come out without 

 further care, or build shallow nests in the river-mud, over 

 which they sit, as our. Promotis does. It ought also to be 

 observed that these sitters are among the brightest spe- 

 cies in their respective families ; for instance, Hygrogonus 

 is bright green, with large black ocelli, encircled with the 

 most brilliant red." Whether with all the species of 

 Chromids it is the male alone which sits on the eggs is 

 not known. It is, however, manifest that the fact of the 

 eggs being protected or unprotected, has had little or no 

 influence on the differences in color between the sexes. 

 It is further manifest, in all the cases in which the males 

 take exclusive charge of the nests and young, that the 

 destruction of the brighter-colored males would be far 

 more influential on the character of the race, than the de- 

 struction of the brighter-colored females ; for the death 

 of the male during the period of incubation or nursing 

 would entail the death of the young, so that these could 

 not inherit his peculiarities ; yet, in many of these' very cases 

 the males are more conspicuously colored than the females. 

 In most of the Lophobranchii (Pipe-fish, Hippocampi, 

 etc.) the males have either marsupial sacks or hemispheri- 

 cal depressions on the abdomen, in which the ova laid by 

 the female are hatched. The males also show great at- 

 tachment to their young. 36 The sexes do not commonly 



35 ^Yarrell, 'Hist, of British Fishes,' vol ii. 1836, pp. 329, 338. 



