xiii PHYLUM CHORDATA 293 



with a t3'Dipanic membrane. The etlerent ducts of the testis 

 open into the urinary tubuh^s, and the mesonephric duct of tlie 

 male is a urinogenital duct. In the female the mesonephric ducts 

 become the ureters, and the oviducts are pronephric ducts with 

 coelomic apertures. The proneplnos is the functional kidney in 

 the larva, the mesonephros in the adult. There is an allantoic 

 bladder. Developjnent is usually accompanied by a metamorphosis, 

 the young being hatched in the form of a branchiate larva. 

 The Amphibia are classified as follows: — 



OiiDEPv 1. Urodela. 



Amphibia which retain the tail throughout life. There are 

 usually two pairs of limbs of approximately equal size. 

 The order is conveniently divided into — 



a. Perennihrancliiata, which retain the oriUs throughout life : 

 including the American Xcdurus, i\\e.h\m(\ Pivteus oi the under- 

 srround caves of Carniola in Dalmatia, and the Eel-like Siren of 

 North America. 



b. Derotremata , in which the gills ai'e lost in the adult, but 

 there is usually a persistent gill-cleft : including the Newt-like 

 Cryptohr(i7ichi(s and the Eel-like Amphiuma from North America, 

 and the Giant Salamander, Ilajalohatraclms, of China and 

 Japan. 



c. Myctodera, the Salamanders and Newts, in which the gills 

 are lost and the gill-clefts closed in the adult : including the 

 common Newts or Efts {Molgc), the Spotted and Black Sala- 

 manders {Salawandra) of the European Continent, and the 

 American Amhlystoma, the sexually mature larva of which is the 

 well-known Axolotl. 



Order 2. — Anura. 



Amphibia having no tail in the adult condition. The trunk is 

 short and broad, and the hind-limbs greatly exceed the fore-limbs 

 in size. Gills and gill-slits are never present in the adult. 



Including the Frogs and Toads. 



Order 3. Gymnophiona. 



Snake-like Amphibia having neither limbs nor tail. A dermal 

 exoskeleton is present. There are no gills or gill-slits in the 

 adult. 



Including the Ciecilians (Caxilia, Ejncrium, &c.). 



Order 4. Stegocephala. 



Extinct tailed Amphibia, often of great size, having usually 

 two pairs of limbs and a well-developed dermal exoskeleton. The 

 group ranges from the Permian to the Trias. 



VOL. II T 



