Class MAMMALIA 



See definition of the class, on page xi. 



Subclass EUTHERIA 



All mammals exclusive of the Monotremes. 



Order MARSUPIALIA. MARSUPIALS 



Mammals of small to large size, the young of which are born 

 at a very incomplete stage of development and are usually 

 carried by the mother in an external abdominal pouch. In 

 some members of the order the pouch is rudimentary or even 

 absent, but in the species found in the United States it is well 

 developed. Brain of a low order; a true allantoic placenta 

 rarely present (never in American forms); clavicle present; 

 mammas always abdominal ; teeth numerous and primitive in 

 character; diet varied; habit arboreal, terrestrial, aquatic or 

 fossorial. 



Fig. I. Opossum 



