420 FISHES CHAP. XV 



(" sexual dimorphism " ^). As mentioned above, females are usually 

 larger as well as more numerous than the males, although in one or 

 both respects the reverse may be the case. Secondary sexual char- 

 acters are best marked in Teleosts, where they are generally related 

 to the special role which each sex takes in the deposition and 

 fertilisation of the eggs, and the nurture and protection of the 

 young, of which examples have already been given. To a more 

 limited extent they may be associated with the struggle of the 

 males for the females, and in at least a few Teleosts the 

 exuberant coloration of the males in the breeding season suggests 

 that instances of courtship and sexual selection are not altogether 

 wanting.^ 



Although the vast majority of Fishes are dioecious, instances 

 of functional hermaphroditism are not unknown in a few Teleosts.^ 

 Species of the Percoid genus Serranus (e.g. S. cahrilla, S. hepatus, 

 and S. scriba) are invariably hermaphrodite and self-fertilising. 

 Clirysoplirys auratus is an example of successive hermaphroditism, 

 the male and female sex-cells ripening alternately. As an 

 occasional variation hermaphroditism has been recorded in several 

 other Teleosts, including amongst others such well-known Fishes 

 as the Cod, the Mackerel, and the Herring. The relations of 

 the gonads in hermaphrodites is subject to much variation. 

 In the Cod, for example, the testes may be double, each being 

 continuous with the hinder end of the ovary of its side, or there- 

 may be only a single testis confluent with the anterior or the 

 posterior portion, or with some other part of the surface, of either 

 the right or left ovary. In other Teleosts individuals occasionally 

 present themselves with a testis and an ovary on opposite sides. 



' For a general account of Sexual Dimorphism in Fishes, see Cunningham's 

 Sexual Dimorphism in the Animal Kingdom, London, 1900, pp. 178-227. Some of 

 the more striking examples of Sexual Dimorphism are mentioned in the chapters 

 dealing with the different families of Fishes. 



^ Holt, "On the Breeding of the Dragonet {Callionymus lyra)" P.Z.S. 1898, 

 p. 281. 



^ Howes, Linn. See. Journ. Zool. xxiii. 1891, p. 539, where references are given 

 to the literature of the subject. 



