304 PHILOSOPHY OF ZOOLOGY. 



creases greatly in bulk when placed in water. The sub- 

 stance termed star-shot-jelly ^ is considered as this glaire 

 brought into that state by a frog having been swallowed by 

 a bird, and the warmth and moisture of the stomach, 

 making the jelly in the oviducts expand so much, that the 

 bird is obliged to reject it by vomiting *. The young or 

 tadpoles, as they are termed, lose the tail, gills and beaks, 

 and acquire four legs, when they reach a certain period, 

 and exchange a dwelling in the water for a residence on 

 land. At the period of this change, the intestines are 

 loaded with fat, which Sir E. Home considers as destined 

 to furnish materials for the development of the parts which 

 takes place -f-. The thumb of the male during the season 

 of sexual intercourse, is furnished with an enlarged knob. 

 The urine is watery, and contains urea \. 



Jaws and palate furnished "with teeth. The skin is 

 smooth, and the hind-legs are longest. 



68. Hyla. Tree-frog. Extremities of the toes expand- 

 ed, with suckers beneath. 



The species are numerous, and climb trees in search of 

 insects. The male has a throat-bag, which is filled with 

 air during croaking. 



69. Rana. Frog. Toes simple. The male has cheek- 

 bags, which are filled with air during croaking. 



The common frog is the type of the genus. The spawn 

 is deposited in masses. The adult animals leap easily. 

 According to old Walton, " the mouth of the frog may 

 be opened from the middle of April till August, and then 

 the frog's mouth grows up, and he continues so for at least 

 six months without eating H."" 



• See Phil. Trans. 1810, p. 212. and 217. 



t Phil. Trans. 1816, p. 301. % PhU. Trans. 1821, p. 98, 



II The complete Angler. Bagster^s 2d Edition, London, 1815, p. 237. 

 Fee likewise Pennant, Brit. Zool. vol. iii. p. 11. 



