366 SYSTEMATIC ZOOLOGY 



tion of North America ; all the remaining families are found 

 only in Australia and adjacent islands, although fossils occur in 



Europe as well. 



The family Didelphidae, the opossums, includes all the Ameri- 

 can marsupials. The majority are not larger than a rat. but 

 our common Virginian opossum, Didelphys virginiana ( Fig. 356), 

 attains the size of the domestic cat; it has a long, scaly, prehensile 







FIG. 357. Pet, inthopus, the rock wallaby, closely allied to the kangaroos (Alter 



Vogt and Sprecht, from Parker and Haswell's Manual.) 



tail. This species, which is one of the largest opossums, has a 

 marsupium ; the period of gestation is from twenty-four to twenty- 

 eight days, and of lactation two months. Some South American 

 opossums which have no marsupial pouch carry the young upon 

 their backs, alter they are old enough to leave the teats. Nearly 

 all are insectivorous or carnivorous in habit, and all are arboreal 

 except the water opossum of Brazil, which is aquatic and has 



