CHAPTER IX. 

 THE FROG (continued}: RESPIRATION AND EXCRETION. 



IN the fifth chapter it was pointed out that a continual 

 waste of substance goes on in the frog's body, the lost 

 material taking the form of three chief waste-products or 

 products of excretion, water, carbon dioxide, and urea. It was 

 further stated that these substances are got rid of by means 

 of the lungs, the kidneys, and the skin. 



The Organs of Respiration. At their anterior ends the 

 two lungs open into, a small, thin- walled chamber (Fig. 44, 

 /. tr. c\ which, as it corresponds both with the larynx or 

 organ of voice, and the trachea or windpipe in ourselves, is 

 called the laryngo-tracheal chamber-, it communicates with 

 the pharynx through the glottis (gt). The walls of the 

 chamber and the edges of the glottis are supported by 

 cartilages (ar). 



The structure of the lung is best made out by distending 

 it with air. and then placing it in formaline or spirit until 

 thoroughly hardened : its walls contain so much elastic tissue 

 that if cut when fresh, it contracts immensely, and its struc- 

 ture is then difficult to see. The inner surface of the lung is 

 raised. up into a complex network of ridges (A, r. Ing], which 

 project into the interior and produce the appearance of an 



