112 ON CLASSIFICATION. 



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 sur- 

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

 quite so much. The chorion presents a band, 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 belongs 

 to the same category. 



Admitting all these difficulties and gaps in our information, it 

 still appears to me that the features of the placenta afford by far 

 the best characters which have yet been proposed for classifying 

 the Monodelphous Mammalia, especially if the concomitant 

 modifications of the other foetal appendages, such as the allan- 

 tois and yelk-sac, be taken into account. And it must be 

 recollected that any difficulties offered by the placental method 

 attach with equal force to the systems of classification based upon 

 cerebral characters which have hitherto been propounded. If 

 any objections, on the ground of general affinities, are offered 

 to the association of Elejrfias, Hyrax, Felis, and Cercopithecus in 

 the same primary mammalian division of deciduate Monodelphia, 

 they are not removed by constructing that primary division upon 

 other principles, and calling it Gijrenceplxala. 



