560 ANURA [CH. 



believed that they were introduced by monks from Europe, who 

 before the Eeformation used to pay periodical visits to England to 

 supervise their property. 



In Canada and the Northern United States there are eight 

 species of Frogs. A species believed to be identical with Rana 

 temporaries is found, but the two commonest are Rana virescens, of 

 a green ground colour with lines of velvety black patches, and 

 the great Bull-frog, Rana catesbiana, which attains three or four 

 times the size of Rana temporaria, and is of brownish-yellow 

 colour, peppered over with minute black dots. Like Rana es- 

 culenta this is essentially a water-frog whereas Rana virescens 

 like Rana temporaria spends much of its time on land. Rana 

 catesbiana is highly valued as a delicacy for the table, and in 

 Canada it is being hunted so much that it is becoming rarer. Rana 

 esculenta as its name implies is extensively eaten on the Continent 

 of Europe and in France it is bred for the table on special farms. 



Order III. Apoda. 



The order Apoda is, as has already been mentioned, dis- 

 tinguished by the entire absence of limbs and the worm-like 

 appearance and habits of its members. In the skeleton the reten- 

 tion of a complete roof of bones over the space between cranium 

 and upper lip, known as the temporal fossa, and the existence of 

 minute bony scales embedded in the dermis, are features retained 

 from the Stegocephala. In accordance with their retiring burrowing 

 habits the members of this order have very small eyes, which in 

 some cases are rendered quite functionless by being concealed under 

 the skin. The internal anatomy is in many respects like that of 

 the Urodela, but the pulmonary arterial arch does not in all cases 

 join the aorta. These animals often live at some distance from 

 water and the larval development is passed through inside the 

 egg-shell, but even there the embryo develops large external gills. 

 The species of this family are restricted to the tropics ; Ichthyophis 

 is found in India, Coecilia in South America, and Hypogeophis in 

 Africa. The extinct Stegocephala have been alluded to many times. 

 Under this confprehensive head are comprised all the fossil Amphibia, 

 remains of which are found in the Coal Measures and the Red 

 Sandstones overlying them. It has been already pointed out that 

 some* of them, like Branchiosaurus, appear in the structure of the 

 vertebral column to be the forerunners of the Urodela, while others, 

 like the Labyrinthodonta, appear to lead on to the Anura. Besides 



