414 FISHES CHAP. 
together in the breeding season, in which they are sometimes 
aided by their power of emitting characteristic sounds, and in the 
case of nest-building Fishes by the still more intimate relations 
of the sexes. Even when the lability to waste is very great, 
compensation may be afforded by exceptional fecundity. The 
copulation of the sexes and the internal fertilisation of the eggs 
occur only in Elasmobranchs and some Teleosts. The copulatory 
organs of Elasmobranchs are the so-called “ claspers ” with which 
the males are provided. Some form of copulation is probably the 
rule in the viviparous Teleosts, where the eggs are fertilised in 
the oviducts, or even while they are still in the ovaries, and the 
young are born alive. As mentioned above, an intromittent 
organ is often formed by the prolongation of the genital or the 
urinogenital orifice into a papilla, or a longer or shorter tube.’ 
Some Cyprinodontidae® (e.g. Anableps) have the anterior part of 
the anal fin modified in the male to form an intromittent organ 
along which the urinogenital canal runs (Fig. 374). In the 
females the genital aperture is covered by a special scale, which is 
free on one side and not on the other. “ The male organ in some 
individuals is turned to the right, in others to the left, and in 
some females the opening beneath the special scale is to the right, — 
in others to the left. Copulation thus takes place sideways, a 
left-sided male pairing with a right-sided female, and vice versa.” * 
The anal fin also forms an intromittent organ in the “ Half-beak ” 
(Hemirhamphus). In a genus (Girardinus) of the same family 
the anal fin is modified to form an apparatus for holding the 
female during sexual congress.* The singular method of fertilisa- 
tion practised by the males and females of Callichthys paleatus is 
referred to elsewhere.’ 
With the exception of the pelagic Antennarius, which builds 
its nest in the Sargasso weed in mid-ocean, nest-building and 
parental solicitude for the young are confined to freshwater 
Fishes and to marine forms with demersal ova. Pelagic ova 
must necessarily be beyond the scope of parental care. As a 
rule it is the male which acts as guardian nurse, the female 
troubling herself but little about the fate of her eggs or her 
1 Guitel, Arch. Zool. Expér. et Gén. (3), i. 1893, p. 611. 
2 Garman, Mem. Mus. Comp. Zool. xix. 1895, No. 1, p. 11. 
5’ Cunningham, op. cit. p. 358. 
4H. y. Jhering, Zeitschr. wiss. Zool. xxxviii. 1883, p. 468. ° See p. 592. 
