308 CLASS AMPHIBIA. 



The body is without a tail, and the vertebral column is short, 

 consisting only of nine vertebrae and a urostyle. On the head 

 are the wide mouth and the large eyes, the iris of which has 

 usually a golden lustre. The eyelids are well developed and 

 the lower, which is transparent, can be drawn as a nictitating 

 membrane completely over the eye. The nasal apertures are 

 placed far forward on the extremity of the snout, and can be 

 closed by membranous valves. In the auditory organ there is 

 generally a tympanic cavity, which communicates with the 

 buccal cavity by a short wide eustachian tube and is bounded 

 externally by a large tympanic membrane, which is sometimes 

 free and sometimes concealed beneath the skin. The tongue 

 is absent in the Aglossa ; it is usually attached between the 

 rami of the lower jaw in such a way that its posterior part is 

 completely free, and can be protruded as a prehensile organ. 

 Ribs are as a rule absent, but the transverse processes of the 

 vertebrae may attain a considerable length. Pectoral and 

 pelvic girdles and limbs are always present. The pelvic girdle 

 is distinguished by the styliform elongation of the ilium. In 

 the skin, which is scaleless, glands with an acrid milky secretion 

 are often aggregated in many places, especially in the region of 

 the ear, where they form large projections (parotoids). Glandu- 

 lar aggregations occur also on the middle divisions of the hind 

 legs (Bufo calamita) and on the sides of the body. Reproduction 

 usually takes place in the spring, but Australian frogs spawn 

 when external conditions of moisture allow of it. Sexual con- 

 gress is confined to an external approximation of the two sexes 

 and almost always takes place in the water. The male, which 

 sometimes has a wart-like elevation on the hand (Rana) or 

 gland on the arm (Pelobates), embraces the female from the 

 back, usually with the front limbs, and pours out the seminal 

 fluid over the spawn as it issues in strings or in clumps. The 

 individual eggs are surrounded by a viscous layer of albumen 

 which swells up in the water. The larvae have the form of 

 tadpoles. 



Some Batrachia are purely land animals (toads and tree-frogs), 



berg, 1758. Daudin, " Histoire naturelle des Eainettes, des Qrenouilles^ 

 et des Crapauds" Paris 1802. Rusconi, " Developpement de la grenouille 

 commune," Milan, 1826. C. Bruch, " Beitrage zur Naturgeschichte u. 

 Classification der nackten Amphibien," Wurzburger naturg. Zeitschrift* 

 .1862 and 1863. Boulenger, Ecker, Gadow, loc. cit. 



