EDWARD D. COPE. 79 



tures ; for unlike the marsupial line, the earliest denti- 

 tions are the most simple, and the later the more com- 

 plex. Some of the types retain the primitive trituber- 

 cular molars, as the Centetidse, shrews and some lemurs, 

 and many Carnivora, but the quadritubercular and its 

 derivative forms are by far the most common type in the 

 recent fauna. The forms that produced the complicated 

 modifications in the Proboscidia and Diplarthra ap- 

 peared latest in time, and the most complex genera, Bos 

 and Equus, the latest of all. The extreme sectorial 

 modifications of the tri tubercular type as seen in the 

 Hysenidse and the Felidse, are the latest of their line also. 



Some cases of degeneracy are, however, apjmrent in 

 the monodelphous Mammalia. The loss of pelvis and 

 posterior limbs in the two mutilate orders is clearly a 

 degenerate character, since there can be no doubt but 

 that they have descended from forms with those parts of 

 the skeleton present. The reduction of flexibility seen 

 in the limbs of the Sirenia and the loss of this character 

 in the fore limbs of the Cetacea are features of degen- 

 eracy for the same reason. The teeth in both orders 

 have undergone degenerate evolution ; in the later and 

 existing forms of the Cetacea even to extinction. The 

 Edentata appear to have undergone degeneration. This 

 is chiefly apparent in the teeth, which are deprived of 

 enamel, and which are wanting from the premaxillary 

 bone. A suborder of the Bunotheria, the Ta3niodonta 

 of the Lower Eocene period, display a great reduction 

 of enamel on the molar teeth, so that in much worn ex- 

 amples it appears to be wanting. Its place is taken by 

 an extensive coat of cementum, as is seen in Edentata, 

 and the roots of the teeth are often undivided as in that 

 order. It is probable that the Edentata are the de- 

 scendants of the Treniodonta by a process of degeneracy. 



Local or sporadic cases of degenerate loss of parts are 

 seen in various parts of the mammalian series, such as 



63 



