1881.] NATURAL SCIENCES OP PHILADELPHIA. 141 



While the placenta does not appear to me to have the importance 

 attached to it by some authors as a guide in determining the 

 affinities of animals, it is proper to mention in this connection that 

 according to Milne Edwards^ and Garrod^ the placenta of the 

 Hippopotamus is diffuse and appears to be non-deciduous, and such 

 is the case, according to Harting,^ in the Dugong,* and therefore 

 in the Manatee, probably, for as a matter of fact the placentation 

 of the Manatee is unknown. 



While the brain of the Hippopotamus appears to be a modifi- 

 cation of a type common to the Pig, Peccary, Sheep, Ox, Giraffe, 

 etc., it has also, it seems to me, affinities with that of the Manatee. 

 In a word, then, beginning with the Pig, we pass by an easy transi- 

 tion to the Peccar}^, which leads to the Hippopotamus, and thence, 

 in diverging lines, to the Ruminautia on the one hand, and the 

 Manatee on the other. Paleontologists have not discovered a 

 form which bridges over the gap between the Hippopotamus and 

 the Manatee, but it will be remembered that certain fossil bones, 

 considei'ed by Cuvier^ to have belonged to an extinct species of 

 Hippopotamus, H. medius, are regarded by Gei'V'ais" as the remains 

 of the Halitherium fossile, a.n extinct Sirenean, of which order the 

 Manatee is a living representative. According to Prof. Owen,^ 

 the molar teeth also, both in the Halitherium, and the Felsino- 

 therium,^ another Sirenean, are constructed on the same pattern 



1 Physiologie, Tome 9, p. 56. 



2 Proceed. Zool. Soc, 1873, p. 821. 



■■' Tijdschrift der Nederlandsche Dlerkundige Vereenigung, Deel iv, 1879, 

 p. 1. 



* Dr. Hartung, in his very valuable paper on the placenta of the Dugong, 

 just refeiTed to, describes and figures bodies attached to the blood-vessels 

 resernbling. apparently, very much those of the placenta of the Elephant. 

 His figure (7) shows that the cavity of the vessel communicates with that 

 of the body attached to it. Dr. Harting inquires whether such is the case 

 in the Elephant. I will state in reply, that neither Dr. J. Gibbons Hunt 

 nor myself found any such continuity between the vessel and body in the 

 placenta of the Elephant, These oval bodies in the Elephant are not sacs 

 or cavities, the little branches from the main vessel only ramify through 

 their substance. There seem?, then, to be an essential difference between 

 the oval bodies in the placenta of the Elephant and in that of the Dugong. 



^ Ossemens Fossiles, II, p. 492. 

 ^ Paleontologie Francaise, p. 143. 

 " Geological Magazine, 1875, p. 423. 



* De Zigno, Sopra un nuovo suienio fossile. Reale Acad, dei Lincei, 

 1877-78. 



