408 FISHES CHAP, 
ducts or into the common sinus, and therefore both ducts 
communicate with the exterior by a urinogenital orifice behind 
the anus. Peritoneal funnels, similar to the functional ovi- 
ducts of the female, are present in the males of the Chrondrostei 
and of Amia. In Teleosts the terminal connexions of the ducts 
tend to become less intimate. The archinephric ducts often dilate 
into a urinary bladder either before or after their union, and 
the common duct joins the united gonoducts to form a short 
urinogenital sinus which opens externally, or the confluent 
gonoducts have an independent genital orifice between the anus 
and the urinary aperture. Not rarely the genital or the urino- 
genital orifice is prolonged into a tubular papilla, which in the 
male acts as an intromittent organ, or, as in the females 
of the Cyprinoid Rhodeus amarus, the long oviducal tube 
serves the purpose of an ovipositor. The males and females of 
the Siluroid Plotosus have a remarkable vascular and glandular 
arborescent appendage just behind the urinogenital papilla, the 
use of which is unknown.’ 
The eggs of different Fishes” exhibit considerable diversity 
in size and shape as well as in the nature of their external 
coverings and their mode of deposition.” The size of the eggs 
largely depends on the quantity of food-yolk stored up in their 
substance for the nutrition of the embryo: hence the eggs of 
Elasmobranchs, which resemble Fowls’ eggs in the superabund- 
ance of their yolk, are by far the largest. Teleostomi have 
much smaller eggs. The largest Teleostean ova are those which 
are heavy and sink (demersal ova); the smallest, those which 
are buoyant and float (pelagic ova). Of the former, the eggs of 
Gymnarchus are about 10 mm. in diameter; those of the Salmon 
about 5 mm.; and those of some species of Arius, 5 to 10 mm. 
The eggs of the Wolf-Fish (Anarrhichas lupus) are about 6 mim. 
Smaller demersal ova are those of the Lump-sucker (Cyclopterus) 
and Heterotis, which are 2°6 and 2°5 mm. respectively. Pelagic 
1 Hirota, Journ. Coll. Sci. Imp. Univ. Japan, vii. 1895, p. 367. 
? For the eggs of Cyclostomes see Chapter XVI. 
3 For a description of the eggs and breeding habits, and the larval develop- 
ment and migrations of British Marine Fishes, see M‘Intosh and Prince, Trans. 
Roy. Soc. Edin. 1890; M‘Intosh, Ann. Report Fishery Board for Scotland, 1892 ; 
Cunningham, Marketable Marine Fishes of the British Islands, London, 1896 ; 
M‘TIntosh and Masterman, Life-Histories of the British Marine Food- Fishes, 
London, 1897 ; also numerous papers by Cunningham, Holt, Garstang, and Allen, 
in the Journ. Marine Biol. Assoc. Plymouth, vols. i.-vi. 
