SIR WM. TURNER ON THE PLACENTATION OF HALICORE DUGONG. 655 



into corresponding recesses. As the Mare and Cetacean are typical examples of mammals 

 with a non-deciduate placenta, the Dugong also in the general scheme of its placenta 

 without doubt resembles them. But my description has shown that, in addition to the 

 multitudes of short villi and shallow crypts, the Dugong also possessed a small proportion 

 of longer villi, which were implanted in longer, wider, and more deeply seated crypts, 

 passing for some distance in an oblique direction subjacent to the layer of short crypts. 

 From the fact that in the separation of the maternal from the foetal part of the placenta 

 which had occurred before I opened the uterus; these longer villi had torn away from the 

 chorion, and had remained implanted in the more deeply seated crypts, it is evident that 

 the villi were more difficult to draw out of the crypts, and it is possible, therefore, that 

 in the normal act of parturition, when these villi separate along with the rest of the 

 foetal placenta, they may drag away the vascular walls of the maternal crypts in which 

 their bulbous ends are implanted. Should this be the case, then the placenta of the 

 Dugong would in a limited sense be deciduous, though in far the greater part of its area 

 it would, as already stated, be non-deciduate. If I am right in this supposition of the 

 shedding of the vascular walls of those maternal crypts in which the longer villi are 

 inserted, whilst the shorter crypts retain their attachment to the uterus, then the 

 placenta, whilst in the main non-deciduate, would furnish an example of the commence- 

 ment of the deciduate type, and would illustrate the transition from a non-deciduate 

 placenta to the more perfect deciduate type seen in the Carnivora and other zono- 

 placental mammals. Should, however, these larger villi separate from the maternal 

 placenta without taking with them the vascular walls of their crypts, which I think is 

 the more likely, the placenta would be throughout non-deciduate. The placenta of the 

 Dugong would then furnish us with a new type of placenta, one which is both zonary 

 and non-decicluate. The presence of these two characters, hitherto unknown as existing 

 in combination in any placenta previously examined, teaches us that the similarity in form 

 which the Dugong's placenta bears to that of the Carnivora and Seals does not necessarily 

 imply a correspondence in the intimate relations of the structural elements. We cannot 

 therefore predicate whether a placenta is deciduate or non-deciduate from the study 

 merely of its external form. 



In the discussion of this question I have used the term deciduate in the sense in 

 which it is usually employed to express the shedding of the vascular part of the maternal 

 placenta during parturition. In a communication made to this Society a Dumber of 

 years ago,* I showed that both in the Sheep and Cow the epithelial lining of the uterine 

 crypts was to some extent shed along with the tufts of the foetal villi. It is not unlikely 

 that a partial shedding of this epithelium may also take place in the Dugong, for, as I 

 have already explained (pp. 645, 650), not only were the epithelial cells in many cases 

 loose in the crypts, but others had become so far detached as to be intermingled with 

 the villi of the chorion. 



* Proc. Roy. Soc. Edin., May 1875; and Lectures on the Comparative Anatomy of the Placenta, p. 108, Edinburgh, 

 1876. 



