100 PROFESSOR TURNER ON THE PLACENTATION OF THE SLOTHS. 
them, either in the decidua or in the fully-formed placenta.* Of the condition of 
the glands, in the early period of gestation in the sloth, we have no information, 
but that they are absent in the later period I have little doubt, for the careful 
examination to which I subjected both the placenta and the non-placental area 
of the mucosa would have disclosed them had they been present. 
Both in the sloth and in the human subject the decidua reflexa is well 
marked. The serotina is not, however, so strongly developed in the sloth; 
more especially is there a deficiency in the granular colossal cells, which in the 
human placenta not only lie on its uterine aspect, but pass into its substance 
in the decidual dissepiments. 
The great importance in foetal nutrition, which has been ascribed by 
ErcoLani in his several valuable and most instructive memoirs on placental 
structure to a system of gland follicles forming the maternal part of the placenta, 
which he believed to be new formed during pregnancy in all placental mammals, 
and in which the foetal villi are lodged, naturally led me to examine the sloth’s 
placenta with care, to ascertain if in it such gland follicles could be recog- 
nised. I failed, however, to see any indications of follicular structure, either in 
the defined form described by him to exist in the diffused cotyledonary or 
zonary placenta, or as a layer of cells, belonging to the decidua serotina, 
investing the foetal villi as in the human female. 
I have already, in my memoir on the Placentation of the Cetacea,t criticised 
and advanced some objections to the general applicability of ErcoLant’s 
theory, and from the study of the placenta in the sloth there appear to be addi- 
tional reasons for doubting that anatomical unity in placental structure which 
he advocates. The presence of a gland secretion as an osmotic medium in foetal 
nutrition, whether we regard it as produced by new-formed gland follicles, as 
ERcOLANI supposed, or by the utricular glands themselves, as Escuricut argued, 
does not, I believe, necessarily occur in all forms of placente. That a white 
fluid, subsequently termed uterine milk, which serves as aliment for the foetus, 
is present in the cotyledons of the ruminants was known to Harvey and the 
older school of physiologists, and it is very probable that a similar fluid is pro- 
duced in all placentz where uterine glands or follicles continue to secrete dur- 
ing the whole period of placental formation. But in those placente, as the 
sloth, the apes, and the human female, where an unusual development of the 
maternal blood-vessels into large sinuses takes place, a modification in the 
anatomical structure is introduced which seems to render the presence of such 
a secretion unnecessary ; the utricular glands seen in the non-gravid uterus 
* Dr Prizsriey states (p. 27) that he could see them distinctly in the parietal decidua near the 
seat of the placenta in the 3d month, but they were undergoing granular degeneration, and, instead of 
being lined with epithelium, were filled with granules and molecules. 
+ Trans. Roy. Soc. Edinburgh, vol. xxvi. p. 467. 
