4 1 4 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 liability 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 introniittent 

 organ is often formed by the prolongation of the genital or the 

 urinogenital orifice into a papilla, or a longer or shorter tube. 1 

 Some Cyprinodontidae 2 (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. 4 The singular method of fertilisa- 

 tion practised by the males and females of Calliclithys paleatus is 

 referred to elsewhere. 5 



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. Exper. et Gen. (3), i. 1893, p. 611. 



2 Garman, Mem. Mus. Oomp. Zool. xix. 1895, No. 1, p. 11. 



3 Cunningham, op. cit. p. 358. 



4 H. v. Jhering, Zeitschr. wiss. Zool. xxxviii. 1883, p. 468. 5 See p. 592. 



