THE MOUSE 



439 



Sense-organs. — In addition to certain diffuse senses, such 

 as touch and heat and cold, tlie raljljit has complex organs of 

 taste and smell, hearing and sight. The organs of taste and 

 smell lie in the dedicate hning of the mouth and nose — as small, 

 diffuse sense cells. The ear is essentially like that of man, and 

 differs from that of birds in the greater development of the 

 cochlea, which, in the rabbit, forms a close spiral of two and 

 one-half turns. The eye lacks the pecten, and is more nearly 



Fig. .397. — The duckbill, Ormthorhynchus anaflnus. After Vogt and Specht. 



spherical in shape. There are two ej^elids ; and the nictating 

 membrane, so prominent in birds, is rudimentarj^ 



Mammals are divided into three main groups. The division 

 depends upon the condition in which the 3'oung are born. 

 The lowest group is called monotremes. The mi.'k glands are 

 in a low state of development, and eggs are laid in the shell, as 

 in reptiles and l)irds. There are two principal types, — the 

 "Duckbill " (Fig. .397), with aquatic habits, and the "Spiny 

 Ant-eaters " (Echidna, Fig. 398), inhabiting rocky places. 

 Both types are confined to Australia and neighboring islands. 



