272 ZOOLOGY SECT. 



throughout life : in the non-branchiate species these structures 

 undergo more or less degeneration and give rise to the tongue-car- 

 tilage. The heart has a sinus venosus, right and left auricles, a 

 single ventricle, and a conus arteriosus; the aortic arches arise from 

 a bulbus aortae or abbreviated ventral aorta. The cardinal veins 

 undergo more or less degeneration and are practically replaced by 

 an unpaired post-caval 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 noticeable. 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 the 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 Nect-urus, the blind Proteus of the under- 

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

 North America. 



b. Dcrotrcmata, 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. Mydodera, 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. 



