000 



SIR \VM. TURNER ON THE PLACENTATION OF HALICORE DUGONG. 



at his disposal he regards them as forming a distinct order. He had no knowledge of 

 the form and structure of their placenta, but from the description which I have given 

 of that organ in the Dugong, it is clear that its type of structure is so peculiar as to 

 strengthen the view that the Sirenia have an ordinal value. 



From the study of the placenta of the Dugong it is obvious that in future it will be 

 necessary to arrange the mammals which possess a zonary placenta into two groups : 



ZONO-PLACENTALIA. 



a. Non-deciduata. — Dugong either whole or in great part ; probably also the 

 Manatee. 



b. Deciduata. — Carnivora, Pinnipedia, Elephant, Hyrax. 



WOODCUT. 



The subjoined woodcut is a diagrammatic representation of the arrangement of the foetal 

 membranes, and their relation to the embryo Dugong; p. 648. The embryo has been drawn in the 

 amniotic sac by Mr Gustav Mann. 



Ch, the chorion, with n the zonary placenta. Al, the sac of the allantois; Al', the outer wall of 

 the sac or endochorion; AV, the inner wall of the sac. Am, the sac of the amnion, the 

 membranous wall of which is represented by the Jotted line. 



