SIR WM. TURNER ON THE PLACENTATION OF HALICORE DUGONG. 657 



which small fusiform cells were seen. Within the areolae some cells resembling leuco- 

 cytes were found. These bodies were invariably attached to the coats of the blood- 

 vessels, almost always to the veins, and Harttng regards them as diverticula from the 

 vascular wall. In my older example they were also closely attached to the coats of the 

 umbilical vessels of the endochorion. They were light brown in colour, flattened or 

 plate-like in form, and not subdivided internally into areola?. They were, however, 

 obviously similar structures in the two specimens, and the differences at the two ages 

 were doubtless due to the one being structurally more advanced than the other. 



These allantoic bodies in the Dugong are probably homologous with the well-known 

 " hippomanes" of the Mare, which, though usually found floating in the fluid contents of 

 the allantois, yet arise, as I pointed out some years ago,* in the gelatinous tissue which 

 connects the chorion with the endochorion. They also correspond with the shot-like white 

 spherical bodies which Professor Rolleston t and I have described in the corresponding 

 gelatinous tissue in the Pig ; J which bodies are also attached to the walls of the blood- 

 vessels. Sir Richard Owen has shown the presence of similarly situated bodies in the 

 fcetal membranes of the Elephant § at about the middle of gestation, most numerous 

 near the placenta, and developed in connection with the coats of the umbilical vessels. 

 From a microscopic examination, to which I subjected a specimen some years ago, I 

 found || that it consisted of a tough fibrous tissue in which nuclear-looking particles 

 were imbedded. Dr Chapman of Philadelphia has since described IF the membranes of 

 an Elephant delivered at the full term, and has figured these bodies attached to the 

 umbilical vessels, both veins and arteries, on and near the placenta. He considers 

 them to project towards the amnion, as the allantoic sac had disappeared in the placenta 

 at the full term. He states that they are fibrous in structure, with some interfibrous 

 granular matters. It is difficult to give a satisfactory explanation of the function of 

 the allantoic bodies. 



Neither in Dr Harting's specimen nor in mine were any amniotic corpuscles to be 

 seen, nor was there any evidence of the presence of an umbilical vesicle. 



It will now be of interest to compare the placentation of the Dugong, which may be 

 taken as a type of the Sirenia, with that of those orders of mammals with which the 

 Sirenia have from time to time been regarded as most closely allied. 



By the Messrs Cuvier the Sirenia were grouped with the Cetacea as a suborder, 

 Cetacea Herbivora. Although the Sirenia have without doubt some points of corre- 

 spondence with the Cetacea in their placental relations, they possess many more features 

 of difference. Both orders of mammals have a bicornuate uterus and are uniparous. 



* Lectures on Comp. Anat. of Placenta, p. 26. 

 t Trans. Zoolog. Soc, vol. v., 1863. 



X Lect. Comp. Anat. Placenta. C. Hennig has subsequently published a description of these bodies in the Pig 

 (Sitz. der Naturf. Ges. zu Leipzig, 1877). 



§ Trans. Roy. Soc. Lond., 1857 ; Anat. Vertebrates, vol. iii. 



|| Lect. Comp. Anat. Placenta, p. 27. 



IT Jour. Acad. Nat. Sci. Philad., vol. viii., 1880. 



VOL. XXXV. PART II. (NO. 17.) 5 N 



