ON THE ARRANGEMENT OF THE FGETAL MEMBRANES IN THE CETACEA. 495 



epithelium is flattened, and with the structureless membrane with which it is in 

 contact belongs to the villus, whilst the outer epithelium is cylindrical, and with 

 its structureless membrane constitutes the utricular gland into which an ordinary 

 vascular villus has entered. Further, he states that all the uterine glands do 

 not contain villi, but that some remain free. The appearance described by 

 Jassinsky is obviously the same as that represented by Professor Goodsir in 

 his well-known figure (Plate II. fig. 19). And although that anatomist did not 

 definitely describe the external cells of the villi as the epithelial lining of 

 the utricular glands, yet he stated that they belonged to the decidua, were 

 the remains of the secreting mucous membrane of the uterus, and played the 

 part of secreting cells by separating from the blood of the mother the matter 

 destined for the blood of the foetus. As regards therefore the morphological 

 position and the function of these cells, Jassinsky's observations correspond 

 closely with those of Goodsir, though he employs a somewhat different mode 

 of expression in his description. Similarly the layer of flattened spheroidal 

 cells, which Dr Farre described as forming the sheath or outer case of the 

 villus, obviously corresponds with the external cells of Goodsir and the outer 

 epithelium of Jassinsky, and belongs, therefore, to the decidua serotina, 

 although Farre does not definitely state that it forms a part of that structure. 



Ercolani again considers that the cells of the serotina, or cells of the internal 

 epithelial layer, which penetrate between and surround the chorionic villi in the 

 human placenta, constitute a new-formed glandular organ intervening between 

 the villi and the maternal blood spaces or lacunae, and the cells of which 

 separate from the maternal blood nutritive material to be absorbed by the villi. 

 These cells he considers to be derived from cells, which multiply in great 

 numbers, furnished by the submucous connective tissue of the uterus. Whilst 

 agreeing, therefore, with Goodsir and Jassinsky, in considering the cells of the 

 serotina, which surround a villus, to be concerned in an important way in 

 fcetal nutrition, yet he does not, with the one, regard them as the remains of 

 the uterine mucous membrane, or, with the other, as the epithelium of the 

 utricular glands, but as a new production formed after the period of conception. 



Hence there is a common understanding not only amongst these, but other 

 investigators, as Van der Kolk and Priestley,"' that the villi of the human 

 chorion are invested by cells, which intervene between the vessels within the 

 villi and the maternal blood-vascular system, and which play an important part 

 in fcetal nutrition, though opinions differ as to their mode of origin. 



But the development of a decidua serotina in the placental area, and the 

 intimate intermingling of certain of its anatomical constituents, which are 

 shed at the time of separation of the placenta with the chorionic villi, are not 

 confined to man, but are found in all animals which possess either the discoid 



* Lectures on Gravid Uterus, p. 83. 

 VOL. XXVI. PART II. 6 N 



