726 MAMMALIA. 



in both Europe and America. In S. America, further, fossil mar- 

 supials related to the Dasyuridre occur ; and as these are not known 

 elsewhere, their presence affords a further confirmation of the view that 

 Australia and Patagonia were once connected. 



Sub-class EUTHERIA. 

 EDENTATES. 



The Edentates include a number of very distinct types, 

 which require at least two orders the New World sloths, 

 ant-eaters, and armadillos, the Old World pangolins and 

 aard-varks. The modern forms are specialised survivors 

 of waning stocks, and they show many interesting pro- 

 tective peculiarities of structure and habit which secure 

 their persistence. Thus some are arboreal, others are 

 burrowers, and many are covered with strong armature of 

 bone or of horn. 



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, whose relations to each other 

 and to the other Edentates are exceedingly uncertain. 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 char- 

 acters of Edentates concern the dentition. Functional teeth may be 

 absent, but the ant-eaters (Myrmecophagidse) 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 fore part 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, 

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

 appears. 



The placenta shows much variation in character throughout the order, 

 but the reproductive phenomena are somewhat 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 dis- 

 coidal. 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 suppres- 

 sion of the polar villi of a diffuse type, it is zonary, and doubtfully 

 deciduate. 



