82 FBOGS AND TOADS. 



Feel the rough or warty surface of the skin. These 

 warts are the seat of a bitter substance which is poured out 

 by the toad when it is taken in the mouth of any animal. 

 Snakes do not appear to heed this, but most animals reject 

 the toad because of this acrid secretion of the skin, which 

 the toad can pour out at will. This is its most effective 

 means of protection. If you look at the sides of the toad's 

 head behind the eyes you will see a pair of thickened 

 ridges like long pads beneath the skin. These are special- 

 ised regions of the skin for producing this protecting fluid. 

 Organs which produce special substances for the use of the 

 body are termed glands. Hence we may note the skin of 

 the toad as a glandular skin. 



Further, it is of some importance to note that on this 

 skin there is no kind of covering or protecting growth. 

 This character is noteworthy, since if we look around us 

 we observe that backboned animals with naked skins are 

 remarkably rare. Of the animals likely to be familiar to 

 pupils, only relatives of the toad (e.g. frogs and newts) and 

 the river lamprey can be placed in the category of naked 

 skinned vertebrates. (Incidentally we might here digress 

 to name different kinds of skin outgrowths hair, spine, 

 bristle, feather, scale, with examples.) 



Next, gently lift the toad by the skin of the back, noting 

 how loose is the attachment to the underlying parts. This 

 feature is much more marked in the frog. Beneath the 

 skin are large spaces filled with lymph fluid, and in the 

 frog at the hinder end of the body may be seen the beating 

 of a pair of " lymph hearts," where the lymph fluid passes 

 into the veins. 



One of the striking features of the Amphibian Class is 

 the various changes undergone in mode of breathing. 

 Early in the course of their life-history Amphibia breathe 

 by means of their skin, and notwithstanding the acquisi- 

 tion of other respiratory organs they continue to some 

 extent to make use of their skins for this purpose. In 

 hibernation the lungs are not used for breathing. Although 

 by a mere examination we cannot demonstrate the respira- 

 tory character of the toad's skin we must note this as one 

 of its functions. 



