IXTEHKELATIONR OF THE MESONEPHROS, ETC. 199 



conjugate placenta of the cat, then, there is the same hick o^ 

 provision for an osmotic interchanoe })et\veen motlier and fetus 

 as in the apposed phicentae of the pig and the sheep. Tlius in 

 the placentae whether apposed or conjoined, of all the animals 

 here studied which retain functional mesonephric glomeruli until 

 the renal glomeruli are active, the thin plates of fetal epithelium 

 are absent at all periods of gestation. 



The placenta of man is of the conjoined type with free floating 

 villi of vascular fetal mesoderm co\ered by an ectodermal epithe- 

 lium. The nature of this epithelium is well known from the 

 researches of many authors. At first it is of two layers, the inner 

 cellular, the outer syncytial, with more deeply staining proto- 

 i:)lasm and many nuclei. Originally very irregular, this syncy- 

 tium assumes during the first and second months a more epithe- 

 lial character, so that each villus shows clearly the two separate 

 layers. Later degenerative processes set in; portions of the 

 cellular layer disappear in places, leaving the syncytium as the 

 only covering; the syncytium itself becomes changed in part 

 into the 'cell knots' and 'canalized fibrin' of Minot. Degenera- 

 tive vacuoles may appear in the syncytium later in pregnancy. 

 The fetal capillaries approach nearer to the epithelium, running 

 close to the bases of the still healthy portions of the syncj^tium, 

 as they do in the active part of any gland. The surface of the 

 chorion and its villi is so enormous in the human placenta that 

 apparently much of it may become degenerated without destroy- 

 ing its functional ability to too great an extent, and the areas 

 of functional epithelium may be widely separated by the inacti\e 

 areas of canalized fibrin. 



It is probably on account of the great surface area presented 

 in the himian placenta and the consequent utilization of only 

 small portions of it for active functions that the membranous 

 plates formed by the syncytial layer in conjunction with the fetal 

 capillaries have not been heretofore mentioned or figured, to 

 nw knowledge. A little search is necessary to find the scattered 

 plates, but thej^ may be encountered in all parts of the labyrinth. 

 Perhaps their relative infrequency, as compared with those found 

 in the rodent placenta, is another expression of the small amount 



