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 réle 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. cabrilla, S. hepatus, 
and S. seriba) are invariably hermaphrodite and self-fertilising. 
Chrysophrys 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. 
1 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. 
2 Holt, ‘‘On the Breeding of the Dragonet (Callionymus lyra),” P.Z.S. 1898, 
p- 281. 
3 Howes, Linn. Soc. Journ. Zool. xxiii. 1891, p. 539, where references are given 
to the literature of the subject. 
