378 Vertebrata. 



Dipnoans, the urinary ducts open into the cloaca; in others they unite 

 and open behind the anus, either together with the gonaducts, 

 ■or by a special aperture behind the genital pore. The last is the case 

 in most Teleostei, where there are three openings, one behind the 

 other j first the anus, then the genital pore, finally the urinary 

 aperture* 



In the Teleostei the urinary (and the genital) aperture is usually 

 situated on a small, soft process, the papilla urogenitalis. The 

 posterior portion of the urinary duct is usually wide, and forms 

 a bladder: in the Selachians a pair of bladders is present ; in 

 the Teleosteans one only, an expansion of the common portion of the 

 ducts. 



Female genitalia. In Selachians, Ganoids,t and 

 Dipnoans, the ovary resembles that of most other Verte- 

 brata, and there is a pair of Miillerian ducts, each usually 

 opening anteriorly into the body-cavity b3'' a funnelj ; in the 

 Selachians and Dipnoi they open posteriorly into the cloaca, whilst 

 in the Ganoids they unite with the excretory duct, and open behind 

 the anus by an unpaired aperture. In the Selachians there is on 

 each oviduct a swollen portion with glandular walls, which secrete 

 the horny capsule, surrounding one or more eggs in most of 

 these animals. In the Teleostei, Miiller's ducts are altogether 

 wanting ; the ovaries are hollow and vary in form ; each is 

 prolonged into a short, tubular duct, which unites with its fellow 

 of the other side to open behind the anus. The ovary thus displays 

 relations extremely different from those of all other Vertebrata, but 

 similar to those occurring in many lower animals, e.g., the Mollusca. 

 The ova break away from the much-folded inner wall, and fall into 

 the cavity of the ovary, escaping to the exterior through the duct. 

 The two ovaries are frequently fused posteriorly {e.g., in the Cod), or 

 throughout their whole length (as in Zoarces) ; and the duct is then 

 unpaired. When ripe, in the spawning season, the Teleostean ovaries 

 are often extremely large. 



Only two families differ from the condition just described. In tie Salmon 

 and the Bel tte ovaries ai-e solid, the eggs fall into the body-cavity, and 

 escape by an unpaired opening § in the body- wall, behind the anus (porus geni- 

 talis). The Cyclostomes, which only possess a single ovaiy, ai-e otherwise 

 similar to the Salmonidse. 



* In some Fish, viz.. Selachians, Ganoids, and certain Teleosteans (the Salmon 

 family) there is in this region, on either side of the anus, a pair of small openings, 

 the so-called abdominal pores, which perforate the body- wall, and put the 

 body-cavity in communication with the exterior. Their significance is unknown. 



t With the exception of Lepidosteus, which seems to resemble the Teleostei. 



X In the Selachians the Miillerian ducts are united anteriorly, so that there is only 

 a single funnel for the two. In some Sharks only one ovary is developed. 



§ Which is not to be confounded with the abdominal pores mentioned above (*). 



