Glass 2. Pisces. 379 



Male genitalia. In tlie Selachians tlie spermatozoa 

 escape by tlie anterior portion of the kidney, often termed 

 epididymis; this is in connection with the testis, and the duct 

 arising from it unites posteriorly with those from the rest of the 

 kidney, and serves really as a seminal duct, for the epididymis is 

 of very slight importance in excretion. In the females, also, this 

 region is very little developed. In the Ganoids, too, the sperm 

 makes its way out through the kidney ; numerous transverse canals 

 run from the testis to the kidney (of which no part is specially 

 modified), to communicate with the urinary tubules.* In the 

 Teleostei such a connection with the kidney does not occur, 

 the testis is prolonged directly into a seminal duct,t and like the 

 ovaries, the ripe testes are tolerably large, elongate, often lobed, 

 or {e.g., in the Cod), pleated bodies ; the vasa deferentia unite 

 behind to form an unpaired duct, which has, in some forms, 

 a special opening behind the anus, in front of the urinary 

 aperture, whilst in other cases there is a common urino-genital 

 opening. 



In tte Cyclostomes, the spermatozoa from the unpaired testis fall into the 

 body-cavity, and escape tkrongh an opening of the abdominal wall just as do the 

 ova. 



Copulatory organs occur in all Selachians, where a portion 

 of the hind limb in the male, is modified into a somewhat compli- 

 cated rolled organ (Fig. 314), which is used in copulation [cf. the 

 copulatory organs of decapod Crustaceans). On the other hand, 

 copulatory organs are absent from most other Pish, and the sper- 

 matozoa ("milt") are. usually not introduced into the body of the 

 female, but are poured over, or near to, the eggs when they are laid. 



In certain viviparous Teleostei (Anahleps) there is a long process behind 

 the anus, ivith the urino-genital opening at its apex. This process, which 

 sei-ves as a copulatory organ, is the metamorphosed anal fin, which has 

 fused with the urino-genital papilla. There are siniilar organs in some other 

 viviparous Teleosteans. In all viviparous Fish there must, of course, be a direct 

 transference of the spermatozoa from the male to the female, but copulatory 

 organs are by no means always present. 



Not a few Fish display striking sexual dimorphism; in the males 

 certain fins may be specially well developed, or they may possess a specially 

 brilliant colouiing. Sometimes (e.g., the Stickleback) the msile is distin- 

 guished by striking colotirs during the reproductive season, which disappear 

 later on. The males are usually smaller than the females {e.g., the Eel). 



For hermaphroditism in Fish, see p. 351. 



The eggs vary considerably in size (from the size of a pin's head 

 to that of a Hen's egg and upwards), they are largest m the Selachians, 

 smaller in the Teleostei, where each is covered by a thin transparent 

 ■vitelline membrane sometimes furnished with a micropyle. The eggs 



* The arrangement of the seminal ducts of the Dipnoi is not understood, 

 t The Salmon and the Eel are like the others in this respect. 



