164 THE ANATOMY OF VERTEBEATED ANIMALS. 



into the genito-urinary duct. In the J^atracliia there is like- 

 wise a genito-urinary duct, and the vasa efferentia run to the 

 inner edge of the kidney and enter it. In £ornhinator igneus 

 and Discoglossus 2^ictiis, the genito-urinary duct receives the 

 urinary products and the spermatozoa, in the same way as in 

 the TIrodela, But, in the Frogs and Toads, the urinary tubuli 

 are gathered together into a special small canal which opens 

 into the genito-urinary duct near its termination in the cloaca, 

 and the vasa efferentia pour their contents into this canal. 

 Under these circumstances, the part of the genito-urinary duct 

 which lies beyond the renal canal may become obliterated, as 

 in the Frogs ; or may persist, and play the part of a vesicula 

 seminalis, as in the Toads. 



In the female Amphibia, the kidneys have, as in the male 

 Frogs and Toads, a renal canal which opens into the lower 

 part of the oviduct. 



It would appear from these facts that the oviduct in the 

 female, and the genito-urinary ducts in the male, Amphibia 

 represent both the Wolflfian and the Mullerian ducts of the 

 higher Yertebrata. 



In most Amphibia the ova are impregnated and hatched 

 outside the body, but internal impregnation and incubation 

 occur in some of the TIrodela. In Pipa the eggs are hatched 

 in pouches of the dorsal integument, while the male Alytes 

 carries them twisted in strings round his legs. 



When hatched, the young are devoid of respiratory organs 

 and of limbs, and are provided with a long tail, by means 

 of which they swim about. Branchial clefts soon make their 

 appearance ; and ciliated external branchial plumes, like those 

 of the perennibranchiate TIrodela, are developed. A pair of 

 suckers are sometimes formed upon the under-surface of the 

 mandibular region, and the jaws acquire horny sheaths. 



A broad opercular membrane is developed in front of the 

 branchial aperture, and, in the ISatrachia, extends over and 

 eventually covers the gills, a rounded aperture persisting for 

 a certain time only on the left side. The anterior pair of limbs 

 is developed before the posterior, but in the Frog they are not 

 so soon visible, being hidden by the opercular membrane. 



The lungs make their appearance as diverticula of the 

 ventral wall of the oesophagus. The nasal sacs are at first 

 mere caecal involutions of the integument, but nasal passages 

 communicating with the mouth are soon formed, and lioii: 

 aerial and aquatic respiration are completely established. 



