/ THE FROG. PHYLUM CHORD ATA 



nucleated and niiicli larger than those of mammals ; they are 

 mostly formed m the kidney and destroyed in the spleen and 



leu. 



T. c 



..■ leu. 



B 



r. c. 



^ \ 



'^^ 



,/ 



<^^' 





\ 



Fig. 293. — Blood of a frog, highly magnified. 



A, Fresh ; B, stained. 

 leu., Leucocytes ; r.c, red corpuscles. 



liver. There are the usual three types of white cell ; lymphocytes, 

 monocytes, and polymorphonuclears. 



ORGANS OF RESPIRATION 



The respiratory organs of the frog are the lungs, the skin, and 

 the mucous membrane of the mouth. The lungs communicate 

 with the pharynx by way of the glottis, which leads into a short, 

 wide windpipe consisting of the larynx or voice organ only, 

 without the long trachea, or windpipe proper, which is found in 

 animals with necks. The walls of this cavity are supported by a 

 pair of flat arytenoid cartilages and a very irregular ring, the 

 cricoid cartilage. The lining of the larynx is thrown into a pair 

 of folds, the vocal cords. Between these is a narrow slit, the rima 

 glottidis, through which the air must pass on its way to and from 

 the lungs. The cartilages are supplied with muscles, by which they 

 can be moved, so as to tighten the vocal cords and bring them 

 close together. In this condition the cords vibrate when air from 



