PROFESSOR W. TURNER ON THE PLACENTATION OF THE APES. 
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of the decidua was so very striking, that when I first examined them I was of opinion 
that they were decidua cells covering the placental surface of the chorion, investing 
the stems of the villi and forming a decidua sub-chorialis, which walled in with 
maternal tissue the maternal blood space at its chorionic boundary. If this view be 
accepted then the more superficial of the sub-chorionic cells would have a different 
origin from those of the deeper layers. Though several arguments might be ad- 
vanced in favour of such a conclusion, yet as through want of material I have only 
had the opportunity of studying these sub-chorionic cells in one particular stage of 
development of the placenta in Mcicacus, I do not definitely commit myself to the 
theory of the decidual origin of the superficial layers of cells. The more so as the 
corresponding though not precisely similar arrangement of cells in the human placenta 
does not apparently exist in the earlier half of placental development, which one would 
be disposed to say it ought to have done if it had been derived from the decidua. 
But whilst there is a difficulty in definitely assigning a decidual origin to the sub- 
chorionic cells, and to the cells enveloping the stems of the villi as they arise from the 
chorion, there can be no doubt that the stratified arrangement of cells surrounding the 
villi at their attachment to the liillock-like elevations of the decidua are derived from 
the decidua, for they can be traced in direct continuity with it.* 
The layer of cells enveloping the lateral and terminal buds and the smaller branches 
of the villi in the Macacus closely resembles the corresponding layer of cells on the 
villi of the human placenta, and consists of somewhat flattened though not squamous 
cells, rectangular in outline, and closely applied to each other by their margins so as 
to form a continuous layer. These cells were apparently first described and figured 
by Mr, DalrympleI in the human placenta, and since that time have attracted the 
attention of all who have studied the minute structure of the villi. As regards their 
homology there is, however, a difference of opinion. By most observers they are 
regarded as an epithelial layer continuous with the general epithelial covering of the 
chorion, and belonging therefore to the foetal part of the placenta. In opposition, 
* When this Memoir was presented to the Royal Society, I had not had the opportunity of reading 
Signor Ercolani’s latest and very important memoir, ‘ Sull’ unita del Tipo Anatomico della Placenta nei 
Mammiferi e nell’ Umana specie’ (Bologna, 1877), a copy of which he has with great courtesy presented to 
me. In this memoir Signor Ercolani gives a diagrammatic representation (Taf. v., figs. 15, 16) of the 
embedding in the human placenta of the end of a fcetal villus in a heap of decidual cells, similar to what 
I have described and figured in Macacus (Plate 49, figs. 10, 11). He also speaks most decidedly in support 
of the decidual origin of the sub-chorionic cells of the human placenta. On theoretical grounds I would 
also support this view of their origin, but I have hesitated in the test definitely to assign this mode of 
origin to these cells, as, through the want of specimens in successive stages of development, I have not 
been able to trace their mode of origin. 
t Medico- Chirurgical Transactions, 1842, vol. xxv., p. 21. Mr. Dalbymple speaks of them as 
nucleated cells, resembling an irregular epithelium. E. H. Weber had previously figured the villi as 
possessing a pellucid margin, but had not recognised that this pellucid border was cellular. See his 
drawing in Wagner’s ‘leones Physiological-:,’ and the copies of the figure in R. Wagner’s ‘Physiology,’ 
translated by Dr. Willis, 1842, fig. cxix. ; and Dr. Balt’s translation of Muller’s ‘ Physiology,’ fig. 231. 
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