PROFESSOR TURNER ON THE PLACENTATION OF THE SLOTHS. fotd) 
solution of potash, it was seen to consist of a stratified squamous epithelium, 
the cells of which had the form of broad, flattened scales, with irregular jagged 
margins, and containing ovoid nuclei. The cells in a given layer were closely 
connected together by the interlocking of their adjacent serrated margins. The 
deep surface of the membrane in the region of the muzzle was irregularly 
pitted, and the pits obviously corresponded to hairs, which, in the progress of 
growth, had indented the deeper surface of the membrane, and even elevated 
its superficial aspect into papillary processes. In some cases these papillze were 
perforated by the tactile hairs, but in others they were still imperforate. Delicate 
threads of a fatty sebaceous substance, obviously the secretion of the sebaceous 
follicles, were not unfrequently, but especially at the auricles and muzzle, con- 
tinuous with the deep surface of the membrane. 
It will now be advisable to express an opinion regarding the nature of this 
very remarkable foetal envelope, and as a preliminary it may be well to ascertain 
if a similar arrangement, either in this or other groups of mammals, has been 
noticed by previous writers, and the views which they held regarding it. Von 
Bakr (op. cit. p. 263) states he has seen in the embryo of the Tardigrada, that 
the epidermis, as in the pig, loosens itself as a complete sac, and appears like a 
second amnion within the amnion. IssEn has observed,* closely investing the 
hair of an embryo sloth, a membrane, which he regarded as a continuation of the 
outermost covering of the umbilical cord, as indeed the amnion: in the embryo 
pig also he recognised an analogous membrane, which formed a _ peculiar 
outer-epidermic layer outside the hairs, which disappears in the later period of 
foetal life. G. Srmon has also describedt this membrane in the embryo pig, and 
pointed out that it consists of squamous cells, such as the epidermis is itself 
composed of; but in a subsequent sentence he states that there is a circumstance 
opposed to the view of its epidermal nature, for beneath it another thin layer 
exists which corresponds to the epidermis. . The nature of this membrane in 
the embryo sloth and pig has also been discussed by BiscHorr, KGLLIKER, and 
REISSNER. 
The fullest description, however, of its structure, mode of arrangement, 
and distribution amongst mammals, has been given by Professor HERMANN 
Wetcxer of Halle,t to whose Memoir I am indebted for the references 
to most of the authorities cited above. WerELCcKER gives to this mem- 
brane the name of Epitrichium. He has seen it in two embryos of Bradypus 
tridactylus, in the foetus of Cholepus didactylus, of Myrmecophaga didactyla 
and jubata, of Dicotyles, the common pig, and probably also in the horse ; 
* See Eschricht’s Essay, “‘ Ueber die Richtung der Haare,” in Miiller’s Archiv., 1837, p. 42. 
‘F Miiller’s Archiv., 1841, p. 370. 
¢ Ueber die Entwicklung und den Bau der Haut und der Haare bei Bradypus, in Abhand. der 
Naturforsch. Gesellschaft zu Halle. Bd. ix., 1864. 
