CHOKDATA 



365 



openings ; and from the succeeding class by the structure of the 

 cenital ducts in the female, for there are two distinct uteri and 

 two vaginae, a condition which obtains in no other group <>i 

 mammals. 



The Didelphia present the widest possible variation in habits 

 of life and size : some are herbivorous, some carnivorous, otli 

 omnivorous, others insectivorous ; some are aquatic, some terres- 

 trial, some arboreal ; they range from animals the size of a rat 

 to the giant kangaroos, which when standing erect arc over two 

 meters in height, while some fossils attained the size of a rhi- 

 noceros. The fur is generally soft and long. Teeth are always 

 present and all are permanent except two in each jaw, which tall 

 out and are replaced by others. The mammary glands are in 

 the abdominal region ; there are thirteen teats in all the op 

 sums and four in the kangaroos and other marsupials; they are 

 always within the marsupial pouch. In the male the scrotum 

 occupies the position of the marsupium, and is consequently 

 anterior to the penis. The young are born in a very immature 

 condition, and are placed by the mother in the marsupium, where 

 they adhere tightly to the teats, from which they derive the 

 nutriment for their further development. In the largest mar- 

 supials, the kangaroos, the period of gestation is only from 

 twenty to forty days, and at the end of that time the embryo is 

 only about two centi- 

 meters long ; then it re- 

 mains in the marsupial 

 pouch for about eight 

 months, until it can take 

 care of itself. The brain 

 of the Marsupialia is 

 relatively small ; they 

 are for the most part 

 timid animals of noctur- 

 nal habits. Their geo- 

 graphical distribution is 

 somewhat remarkable : 

 the opossums are con- V 



fined to South America FlG ' 356- Didelphys virginiana, the Virginian opo: 



(After Vogt and Sprecht, from Parker and H 



and the southern por- Manual.) 



4m 



