SLOTHS AND ANT-EATERS 843 



Sub-Class EUTHERIA 



Edentates 



The Edentates include a number of very distinct types, 

 which require at least two orders — (a) the New World 

 sloths, ant-eaters, and armadillos ; (b) the Old World 

 pangolins and aard-varks. The modern forms are special- 

 ised survivors of waning and probably primitive stocks, 

 and they show many interesting protective peculiarities of 

 structure and habit which secure their persistence. Thus 

 some are arboreal, others are burrowers, and many are 

 covered with strong armature. 



While the existing sloths, ant-eaters, and armadillos are not nearly 

 related to one another, the numerous fossil Edentates found in S. 

 America connect them to a common stock. It is otherwise, however, 

 with the pangolins and the aard-varks. Some authorities separate 

 them (as Nomarthra or Effodientia) from the American Edentates 

 (Xenarthra) ; but according to others there is little evidence that the 

 pangolins and aard-varks are related to each other. In view of the 

 uncertainty, it will be readily understood that few " general characters " 

 of Edentates can be given. Almost the only common characters of 

 Edentates concern the dentition. Functional teeth may be absent, 

 but the ant -eaters (Myrmecophagidce) are the only forms which still 

 appear strictly edentulous. When present, the teeth are uniform, 

 usually simple, without roots, and with persistent pulp. They are 

 never present in the very front of the mouth, and they have not 

 more than hints of enamel. Till recently the dentition was de- 

 scribed as monophyodont, but there is evidence of two sets in Tatusia, 

 OrycteropKS, Dasypus, and others. It is the milk set which dis- 

 appears. 



A common primitive character is the persistence of the testes in the 

 abdominal cavity. 



The placenta shows much diversity, but the reproductive phenomena 

 are imperfectly known. In the sloths and ant-eaters the placenta is 

 usually described as dome-shaped ; but according to some authorities 

 this is merely a stage in the growth of a placenta, which is at first poly- 

 cotyledonary, and later discoidal. The discoidal deciduate type appears 

 again in the armadillos, but in Dasypus among them it is said to be 

 zonary. In the pangolins it is diffuse and indeciduate ; in Orycteropus, 

 apparently by a suppression of the polar villi of a diffuse type, it is 

 zonary, and doubtfully deciduate. 



Order Xenarthra 



I. Bradypodidae — Sloths. — The three-toed sloths (Bradypus) and the 

 two-toed sloths {Cholcepus) are restricted to the forests of 



