98 INTRODUCTION TO CLASSIFICATION. 



of a Kodent; so that most unquestionably, if the placental 

 method of classification is to be adopted, both Elephas and Hyrax 

 must go into the same primary division of the Monodelphia as 

 the Eodentia and Carnivora. 



But are these facts really opposed to the belief that the 

 placenta has great taxonomic value ? 



So far as the elephants are concerned, I must confess 

 that I see no difficulty in the way of an arrangement which 

 unites the Proboscidea more closely with the Eodentia than with 

 the Artiodactyla and Perissodactyla, the singular ties which ally 

 the Elephants with the Eodents having been a matter of common 

 remark since the days of Cuvier. 



I have no hesitation in regarding Hyrax as the type of a 

 distinct order of deciduate Monodelphous Mammalia. Hyrax, 

 in fact, hangs by Rhinoceros mainly by the pattern of its molar 

 teeth, a character which affords anything but a safe guide to 

 affinity in many cases. 



The case of the Edentata presents greater difficulties. In 

 this order, the Sloths have presented a cotyledonary placenta, 

 and the Armadillos have been affirmed to possess a discoidal 

 one. I am not aware that the minute structure of the placenta 

 has been examined in either of these groups ; but I am indebted 

 to Dr. Sharpey for valuable information respecting the placental 

 structure of Manis. The surface of the chorion is covered with 

 fine reticulating ridges, interrupted here and there by round 

 bald spots, giving it an alveolar aspect, something like the 

 inside of the human gall-bladder, but finer. The inner surface 

 of the uterus exhibits fine low ridges or villi, not reticulating 

 quite so much. The chorion presents a baud, free from villi, 

 running longitudinally along its concavity, and there is a corre- 

 sponding bald space on the surface of the uterus. The ridges of 

 the chorion start from the margins of the bald stripe, and run 

 round the ovum. The umbilical vesicle is fusiform. This is 

 clearly a non-deciduate placenta, and the cotyledonary form of 

 that of the Sloth leads me to entertain little doubt that it be- 

 longs to the same category. On the other hand, the placenta 

 of Oryeteropus is discoidal and deciduate. 



It may also be urged that the value of the placenta as 



