3 68 



SYSTEMATIC ZOOLOGY 





pletely divided into two, and is then called a two-horned uterus. 

 The embryo, or fetus, is always nourished in the uterus by means 

 of a placenta (Fig. 358). A cloaca and a marsupial pouch are 

 never present. Nine orders of Monodelphia are pretty generally 

 recognized by zoologists, but the arrangement of these orders, 

 with the exception of the lowest and the highest, is a matter 

 of considerable dispute. 



Order 1. Edentata 



The Edentata (Lat. edentatus, toothless) are characterized 

 by the absence of the incisor teeth, and in some representatives 

 of the order all the teeth are lacking. They are for the most 

 part tropical mammals, inhabiting the southern hemisphere ; 



9, 



FlG. 359. Orycteropus capensis, the aard-vark. (After Vogt and Sprecht, from Parker and 



] laswell's Manual.) 



only one species extends as far north as the United States. 

 The brain is small, they are sluggish in habit and appear very 

 stupid. Two families occur in Africa : one is the aard-vark or 

 ground hog (Fig. 359) of South Africa, a burrowing animal about 

 the size of a hog, sparsely covered with stiff hairs; it remains 

 quiet during the day and emerges at night to feed on ants and 



