VERTEBRATA 179 



SUBCLASS I. Prototheria 



These mammals have but one outlet for the intestine, 

 urinary and reproductive organs, as in birds. They are 

 implacental, and the mammary glands are rudimentary. 

 There is but one order. 



i. Monotremata, This order includes two singular 

 forms, the duck mole (Ornithorhynchus) and spiny 

 ant-eater (Echidna), both confined to the Australian 



FIG. 166. Ornithorhynchus. 



continent and New Guinea. The former has a cover- 

 ing of fur, a bill like that of a duck, and webbed feet. 

 The latter is covered with spines, has a long, toothless 

 snout, like the ant-eater's, and the feet are not webbed. 

 Both burrow, and feed upon insects. The brain is 

 smooth in the ornithorhynchus, and folded in the 

 echidna. In both, the cerebral hemispheres are loosely 

 united by transverse fibers, and do not cover the cere- 

 bellum and olfactory lobes, 47 Both lay eggs which 

 resemble those of birds and from which the young are 

 hatched. 



