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TEXTBOOK OF ZOOLOGY 



may vary. Individual toads of a species may vary widely in color 

 and other characteristics. 



The single vocal sac is a rounded throat pouch which balloons out 

 when the toad calls. The toad does not have internal sacs as does the 

 bullfrog or sacs between the ear and shoulder as does the leopard 

 frog. 



On each shoulder is a large oblong gland known as the parotoid 

 gland, which is not found in frogs. Anterior to it and on the side 

 of the head is the vertically oval tympanum. According to Kellogg, 

 the secretion of the parotoid gland "is an acid irritant causing pain 

 in cuts and producing a bitter astringent sensation in the mouth." 



'^ ^Nr External nares 



>^1 VW^V Preorbital crest 



cS ' ( V^=^^X- - Postorb'ital crest 



" ""^^-V-- Tympanum 

 J-- Parotoid 



Fig. 292. — Dorsal view of head region of a toad to show parotoid glands and 



cranial crests. 



It may act as a poison or, at any rate, as a powerful repellent when 

 the toad is seized by other animals. A dog that picks up a toad 

 lets it go at once and does not soon forget the experience. 



The ridges between the eyes and back of them are known as 

 cranial crests. They are made by the bones of the head and are 

 variously named according to their position. Those between the 

 eyes are known as superciliary or supraorbital; the transverse crests 

 back of the eyes and at right angles to the superciliary crests are the 

 postorbital crests. A crest that is absent in Woodhouse's toad but 

 often occurs in other toads is one running from the postorbital crest 

 to the parotoid gland and known as the preparotoid crest. The paro- 

 toid glands are usually in contact with the postorbital crests in 

 "Woodhouse's toad. 



The toes are about one-third webbed, the webs being fleshy. There 

 are two tubercles on the sole of the foot known as metatarsal tu- 



