2$O ANURA CHAP, 



instance, present in the Malay species R. erytkraea and R. clicd- 

 conota and in the Indian R. corrugata. The tympanum occurs in 

 every stage from a conspicuous, free disc to being quite hidden 

 by the skin. The vomerine teeth either form a pair of tiny, 

 mostly transverse rows, between the choanae, or they are 

 arranged in two oblique series which extend beyond the hinder 

 edges of the choanae. 



The vocal sacs vary greatly. Many species, e.g. R. agilis, 

 have none at all. Most species have a pair of internal sacs, and 

 in comparatively few, about a dozen, these sacs have become ex- 

 ternal, a feature which indicates no relationship of the species 

 thus distinguished, for instance the European R. escidenta, the 

 Japanese R. rugosa, the Indian R. liexadactyla, R. cyanophlyctis 

 and R. chloronota, the Borneaii R. glandulosa, the African R. 

 oxyrliynchus and R. mascareniensis, the Mexican R. montezumae. 

 In JR. esculenta, and perhaps in a few others, even the female has 

 some traces of these otherwise male organs, indicated by slit- 

 like folds of the outer skin below the angles of the lower 

 jaw. 



Nuptial excrescences on the inner metacarpal tubercle and on 

 the inner fingers of the male are common; they reach their 

 greatest development in the Himalayan R. liebigi, the male of 

 which is " remarkable for the extreme thickness of its arms, the 

 inner sides of which are studded with small conical black spines, 

 each supported on a rounded base produced by a swelling of the 

 skin. A large patch of similar spines exists on each side of the 

 breast." ! 



Specific glandular complexes in the skin are mostly restricted 

 to a pair of lateral or dorso-lateral folds ; they are often absent, 

 but a few species, e.g. R. glandulosa of Borneo, R. temporalis of 

 Ceylon, R. elegans and R. albolabris of West Africa, have a pair 

 of large flat glands at the base or inner side of the arms. 



All the species of Rana, except those in the Solomon Islands, 

 spawn in the water, where the development of the tadpoles takes its 

 course. Those of some Indian species, notably R. alticola and 

 R. afghana of the Himalayas, and R. curtipes of Malabar, are 

 very peculiar, being provided on either side of the shoulders with 

 a large oval parotoid-like gland, well defined and crowded with 

 pores ; R. alticola possesses in addition an unpaired, sharply 

 1 Boulenger, Cat. Batrach. Salicntia, p. 22. 



