NATURAL HISTORY. 323 



" I had rather be a toad, and live upon the vapour of a 

 dungeon, than keep a comer in the thing I love for others, 

 uses." SHAKSPKKE. 



clods and stones, where, on account of their dusky colour, they 

 escape notice. When the rain descends, they come forth in 

 hundreds from their hiding places, and hence are supposed to 

 have fallen to earth in a shower. 



1030. How is the bull-frog enabled to make the bellowing noise 

 from which it takes its name? 



This sound is produced by certain portions of the larynx of 

 the animal being convex externally and concave internally, so 

 that when the entrance to the larynx is closed, they form a 

 dome over the windpipe, which, from its vibratory properties, has 

 been compared to a kettle-drum. 



1130. How is the croaking of the frog produced? 



This peculiar sound, which is supposed to be expressive of 

 pleasure, is produced by means of the air which it forces into the 

 globular vocal sacs, which are situated near the corners of the 

 mouth, and causes to vibrate in them. The female being without 

 these organs, produces only a slight noise. 



1032. Why are frogs frequently found dead in dusty roads ? 



Because their skin co-operates with their feeble lungs in 

 the aeration of the blood. This internal respiration can only take 

 place when the skin is bedewed with moisture. For this purpose 

 the frog is endowed with certain glands that secrete a fluid to 

 moisten the skin. In dusty roads this fluid becomes cloggpd 

 with dust, and the respiration of the skin being stopped, the 

 animal dies. 



1033. Why are toads useful in greenhouses and other horti- 

 cultural buildings? 



Because they destroy ants; anl devour earwigs, caterpillars y 

 small beetlfs, slugs, and all insects which chance to fall in 

 their way. 



