NA TURE 



\^Nov. 6, 1873 



THE COMMON 

 III. 



FROG* 



TO prosecute successfully our inquiry " What is a 

 Frog ?" it will be well now to make acquaintance with 

 the more remarkable forms contained in its Ordfr, after 

 which, by considering the other Batrachian orders, we 

 may arrive at a certain appreciation of its Class. 



The Frog's own genus (Rana), which contains about 

 40 species, has its head-quarters in the East Indies and 

 in Africa, but extends over all the great regions of the 



Fig. 7.— Poison Org.in of Thalassophryite reticulnla (after Gunther). 

 I, Hinder half ot the head with the venom-sac of the opercular apparatus 

 in situ. * Place wliere the small.opening in tlie sac has been observed. 

 a. Lateral line and its branches ; b, giil-opening; r, central lin ; d, base 

 of pectoral fin ; e, base of dorsal fin. 2. Operculum, with the perforated 

 spine. 



world, except Australia, and parts more southerly still, 

 and except countries situate above 66' north latitude. In 

 South America, however, but a single species is as yet 

 known to exist. 



Amongst the largest species are Rana tigrina, of India 

 and the Indian Archipelago, and the bull-frog {R. Mu^iens) 



Fig. 8 — Vertical, longitudinal Sect 

 (after Owen). ^, uecp grove ; o 

 exit to the poisi n : /, pulp-cavity 

 tion of a Serpent's Poison-fang {a 



n of the Poisuu-iaug of a Serpent 

 its lower termination, which affords 

 Fig. 9— Magnified Transverse Sec- 

 ") S- groove round which thi 



substance of the tooth (containing /, the pulp-cavity) is bent ; 

 point where the sides of the tooth meet and convert the "groove" 

 into what is practically a central cavity, 



of North America. The latter animal may often be seen 

 in the Gardens of the Zoological Society, where it is fed on 

 small birds — a sparrow being easily engulphed within its 

 capacious jaws. 



The Edible Frog, par e.xcellencc {R. csculoita), is found 

 in England as well as on the Continent of Europe. It is 

 as widely distributed over the old world as is R. tempo- 



'" Continued from vol. viiij p. sis. 



raria, but it is unknown in America. It is easily to be 

 discriminated from the common species (see Fig. 4 on 

 p. 510) by the absence of that dark, sub-triangular patch 

 which extends backwards from the eye in R. icmporaria. 

 The male of R. csculcnta is further to be distinguished 

 from the male of the common Frog by the fact of its 

 having the floor of the mouth on each side, distensible as 

 a pouch — the pouches, when distended, standing out on 

 each side of the head. These pouches are called "vocal 

 sa cs," and no doubt aid in intensifying these animals' 

 croak, which is so powerful that (on account of it and 



m^ 



'ith the pouch partly 



because of the country where they are common) they 

 have been nicknamed " Cambridgeshire Nightingales." 

 Specimens from Cambridgeshire are preserved in the 

 British Museum. 



A large South American Frog {Ceratophrys cornuta), 

 which devours other smaller Frogs as well as small birds 

 and beT?ts. is noteworthy on account of the singular bony 



plates which are enclosed in the skin of its back : a cha- 

 racter which it shares with a small South American Toad 

 {Bracliyceplialus cphippiiim), and which we shall here- 

 after see to be a point of special interest. 



A Frog newly discovered* (of a new genus but 

 one allied to Rana), called Ciinotarsus,f has been 



* The type of this genus is a species which was in my own collection (with 

 no clue to the locality whence it originally came), but is now deposited in 

 the British Museum. It was first described in the Proce;dings of the Zoolo- 

 gical Society for 1S68, under t'le name Piichvhgi,irachus. 



t Proc. Zool. Soc, 1869. 



