94 DR. J. W. JENKINSON ON THE [Feb. 6, 



Creighton, 0. Microscopic Researches on the Formative Pro- 

 perty of Glycogen. London, 1896. 



KoLSTER, R. " Weitere Beitrage zur Kenntniss der Embryotrophe 

 bei Indeciduaten." Anat. Hefte, Ite Abth. xx. 1903. 



Langhaks, T. " Ueber Glycogen in pathologischen Neubildungen 

 und den menschlichen Eihauten." Yirchow's Archiv, 

 cxx. 1890. 



Lassaigne, J. L. " Analyse des hippomanes trouves dans le 

 liqnide contenu dans la membrane de I'vitertis de la vache 

 appelee allantoide." Ann. de Chim. et de Phys. x. 1819. 



Turner, W. Lectures on the Comparative Anatomy of the 

 Placenta. Edinburgh, 1876. 



Postscript. 



Since this paper was read, an important memoir has been 

 published by Assheton ("The Morphology of the Ungulate 

 Placenta, &c.," Phil. Trans. B. 198, 1906), in which the author 

 describes a very complete series of stages in the formation and 

 development of the placenta of the Sheep. 



The most interesting point of this description is the origin 

 of the cells which line the crypts of the maternal cotyledons from 

 the binucleate cells of the trophoblast. 



According to Assheton, the whole of the uterine epithelium 

 degenerates and disappears at about the eighteenth day of 

 pregnancy. In the extra-cotyledonary regions it is eventually 

 regenerated (12th week); but in the cotyledons its place is taken 

 by cells of foetal — trophoblastic — origin, the binucleate cells, which 

 are also, indeed, instrumental in its destruction. The binucleate 

 cells in question are first seen (15th day) to be deeply seated 

 in the trophoblast ; presently, however, they come to the surface 

 and so into contact with the uterine epithelium, between the cells 

 of which they insinuate themselves, and so "pass down to the 

 base of the layer and force themselves between the epithelium 

 and the sublying stroma." The epithelium thus cut off from its 

 source of nutrition dies, and its room is occupied by a more or less 

 complete layer of flattened cells, which Assheton compares to the 

 plasmodiblast layer of the trophoblast described by Yan Beneden 

 in the Bat and Rabbit, and present in many other forms. The 

 formation of this plasmodiblast continues throughout pregnancy. 



In asserting the trophoblastic origin of these cells, Assheton 

 relies on the following facts : — 



(1) They resemble the binucleate cells in the staining capacity 



of their cells and nuclei. 



(2) The presence in them of vacuoles, which is at this stage a 



characteristic of these (the binucleate) cells. 



(3) Nuclei occur in pairs in the lining of the crypts, as in the 



binucleate cells. 



(4) The number of binucleate cells in the trophoblast diminishes 



during gestation. 



