284 ZOOLCXJY SECT. 



right and left auricles, a single ventricle, and a conus arteriosus ; 

 the aortic arches arise from a bulbus aortse or abbreviated ventral 

 aorta. The cardinal veins undergo more or less degeneration 

 and are practically replaced by an unpaired postcaval vein. There 

 is a renal portal system, part of the returning blood from the 

 posterior parts of the body going through it, the rest through the 

 hepatic portal system by an abdominal vein which represents 

 fused lateral veins. The red corpuscles are oval and nucleated 

 and are often of unusual size. The lymphatic system is well 

 developed. In the brain the small size of the cerebellum is notice- 

 able. The olfactory sacs open into the mouth by posterior nares. 

 The outer wall of the auditory capsule is pierced by a fenestra 

 ovalis into which is inserted a cartilaginous stapes : the stapes 

 may be connected by a columella with a tympanic membrane. 

 The efferent ducts of tbe testis open into the urinary tubules, and 

 the mesonephric duct of the male is a urinogenital duct. In the 

 female the mesonephric ducts become the ureters, and the oviducts 

 are pronephric ducts with coelomic apertures. The pronephros is 

 the functional kidney in the larva, the mesonephros in the adult. 

 There is an allantoic bladder. Development is usually accompanied 

 by a metamorphosis, the young being hatched in the form of a 

 branchiate larva. 



The Amphibia are classified as follows : 



ORDER 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. Perennibranchiata, which retain the gills throughout life : 

 including the American Necturus, the blind Proteus of the under- 

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

 North America. 



b. Derotremata, in which the gills are lost in the adult, but 

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

 Cryptobranchus and the Eel-like Amphiuma from North America, 

 and the Giant Salamander, Megalobatrachus, of China and Japan. 



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

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

 common Newts or Efts (Molge), the Spotted and Black Sala- 

 manders (Salamandra) of the European Continent, and the 

 American Amblystoma, 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. 



