654 SIR WM. TURNER ON THE PLACENTATION OF HALICORE DUGONG. 



early stage of development of the human ovum. Then as it becomes elongated the villi 

 disappear from the poles, so that a definite non- villous area appears at each pole, and with 

 the continued growth of the ovum the proportion of the bare spaces to the villous chorion 

 increases. This is apparently the stage of development at which Haeting's specimen 

 had arrived, and it will be observed that he saw not only the naked poles, but the 

 presence of bare patches amidst the villi, which obviously marked the beginning of a 

 further disappearance of these structures. In my specimen the placenta had undoubtedly 

 reached its completed stage of development as a definite zonary band. 



Another point of difference in the chorion at these two stages of development must 

 also be referred to. In Dr Haeting's example there was an appendage covered with 

 villi apparently extending into the non-fecundated cornu. In my specimen no such 

 prolongation was present, and one can see why in the more advanced stage of develop- 

 ment such an appendage was unnecessary. So long as the villi were diffused over a large 

 area of the chorion, there must have been a corresponding diffusion of the crypts in the 

 uterine mucous membrane for their reception. Consequently at this early stage of 

 development, as much of the mucous lining of the non-fecundated cornu as corresponded 

 with the villous surface of the appendage of the chorion w r ould contribute to the forma- 

 tion of the placenta. But with the gradual atrophy of the villi from the poles and from 

 a large part of the surface of the chorion, the corresponding crypts in the mucous 

 membrane would also disappear ; the appendage would become functionally inactive, 

 and would either atrophy, or become, by the great dilatation of the chorion in the gravid 

 horn, incorporated with or expanded into it. 



Another and very important conclusion to which Dr Haeting arrived was that the 

 placenta in the Dugong was indeciduate. This indeed was almost a necessary corollary 

 from its diffused structure, for so far as we at present know every diffused placenta is 

 non-deciduate. But the recognition of the zonary form in the more advanced stage of 

 placental development of the Dugong has introduced another element into the discussion 

 of this subject. Our knowledge of the zonary placenta has hitherto been confined to its 

 presence in the Carnivora proper, the Pinnipedia, Hyrax, and the Elephant. In all of 

 these animals the placenta is deciduate, i.e., when shed in the course of parturition the 

 chorion carries away with it distinctly recognisable portions of the vascular mucous coat 

 of the uterus. On a priori grounds we should expect to find that the Dugong, with its 

 zonary placenta, was also deciduate. I examined the placenta, therefore, with great 

 interest with the view to determine this question. 



The relative shortness of the great majority of the chorionic villi, and the corre- 

 sponding shallowness of the uterine crypts in which these villi had been lodged, together 

 with the cylindriform shape both of villi and crypts and the paucity of their branches, 

 had permitted the separation of the foetal and maternal divisions of the placenta from 

 each other before the uterus was opened into. The separation had apparently taken 

 place as readily as in the Mare or Cetacean, in which animals, though the villi and crypts 

 are short, yet the villi have numerous tuft-like branches, and the crypts are subdivided 



