SIR WM. TURNER ON THE PLACENTATION OF HALICORE DUGONG. 659 



The ungulate affinities of the Elephant have been dwelt upon by various naturalists. 

 This animal has a well-marked zonary placenta, which Sir Richard Owen stated to be 

 in the middle of the chorion, though Dr Chapman in his more advanced specimen found 

 it to be on one side of the middle. In addition, the chorion possessed a small vascular 

 patch of villi diffused at each pole of the chorion. The deciduate character of this 

 placental zone was recognised both by Owen and myself ; and Chapman estimates, from 

 the injection of the blood-vessels in his specimen, that at least one-fourth of the shed 

 girdle-like placenta consisted of the hypertrophied mucous membrane of the uterus. In 

 Owen's specimen the allantois was persistent ; in Chapman's it is said to have disappeared 

 as a distinct sac. Owen makes no mention of an umbilical vesicle, and Chapman states 

 distinctly that he did not find a trace of it. De Blainville regarded the Sirenia as a 

 group of aberrant Elephants, and more recently Dr Murie * has referred to the probable 

 affinities between the Sirenia and the Elephant. 



Many years ago Sir Richard Owen t pointed out that the placenta is not an organ 

 which guides to the true grouping of the Ungulata, and that the modifications of the 

 placenta do not form a true guide to the affinities or classification of the Mammalia 

 generally. In more than one memoir J I have also shown that the placenta cannot be 

 taken as a dominant organ for purposes of classification; yet, in the study of the 

 affinities of animals, its characters require to be considered in conjunction with those 

 of the other organs in the body. In this connection, therefore, it is interesting to 

 observe that, as regards its form, the placenta both in the Elephant and the Dugong 

 is zonary; though they differ in this very important particular, that in the Elephant 

 the zonary placenta is deciduate, in the Dugong it is almost entirely, if not entirely, non- 

 deciduate. 



The zonary placenta possesses its best known form and structure in the Carnivora 

 proper and in the Pinnipedia, in which animals it is usually equatorial in position. In 

 both these suborders it is highly deciduate, although the relative amount of mucous 

 membrane which separates along with the chorion would seem to vary in different species. § 

 All these animals possess a persistent and well-developed allantoic sac, and as far as we 

 at present know they have also a persistent umbilical vesicle. Except in the mere form 

 of the placenta, the Dugong does not seem to have any special affinity with the Carnivora 

 proper, or with the Pinnipedia. 



J. F. Brandt in his great memoir, " Symbolao Sirenologicse," [| compares the Sirenia in 

 their structure and habits with the Cetacea, Pachydermata, Phocacese, and Zeuglodon. 

 Although he considers that in some respects they are more closely allied with the 

 phytophagous Pachyderms than with any other order of mammals, yet from the evidence 



* " Form and Structure of the Manatee," Trans. Zool. Soc. Lond., vol. viii., 1870. 

 t Memoir on the "Placenta of the Elephant" (Trans. Boy. Soc. Lond., 1857). 



X Memoir on the " Placentation of the Sloths" (Trans. Boy. Soc. Edin., 1873, vol. xxvii.) ; and on the " Placentation 

 of the Lemurs," in Trans. Boy. Soc. Lond., 1876, vol. clxvi. 



§ See my Lectures on the Gomp. Anat. of the Placenta, p. 111. 



|| M4m. de VAcad. Imp. des Sciences de St Petersb., 7th series, fasc. ii. and iii., cxii., 1869. 



