DECIDUA VERA AND CH ORION L^E VE OF THE SECOND STAGE. 327 



except that the degeneration is further advanced and the membrane thinner. 

 Traces of cellular structure are still more vague and the fibrin is more developed. 

 In all parts of the membrane there appear leucocytes which are particularly 

 numerous and conspicuous in the neighorhood of the placenta. It is natural 

 to assume that they are concerned in the resorption of the reflexa. There is 

 an inner thicker layer of fibrin and a thinner outer layer, which is now always 

 present and distinct. Between these two layers is a stratum in which the re- 

 mains of the cells may be seen. Occasionally there is an appearance which sug- 

 gests surviving decidual cells, and, indeed, in sections taken from parts close to 

 the placenta true decidual cells may be identified. 



The origin of the chorion laeve and the disappearance of its villi have been 

 described (page 121). The sections of the decidua reflexa will serve also to 

 enable the student to see some of the phases of the degeneration of the. villi. 

 They are very much altered. Their ectoderm undergoes a hypertrophic degen- 

 eration and becomes hyaline tissue, which stains darkly. The degenerated 

 ectoderm of adjacent villi fuses more or less extensively. The mesoderm of the 

 villi shows a partial loss of its primitive cellular organization. 



Decidua Vera and Chorion Laeve of the Second Stage. 



Pieces of the decidua vera of from six to nine months with the chorion and 

 amnion carefully preserved in situ may be hardened in Miiller's or Telly esnicky's 

 fluid. Blocks half an inch or less in size may be imbedded in celloidin and sec- 

 tions made perpendicularly to the surface, stained with alum hematoxylin and 

 eosin, or with Heidenhain's hematoxylin and orange G, or with picro-carmine. 



The decidua reflexa having been resorbed, the chorion (Fig. 189, Cho) has 

 come into contact with the surface of the uterus, and the chorionic epithelium, c, 

 is closely adherent to the surface of the decidua, from which the original epithe- 

 lium has completely disappeared. The amnion is loosely connected with the 

 chorion by ,a few strands or threads, which are represented in the figure and 

 the nature of which is not known. Both the amnion, Am, and the chorion, 

 Cho, being developed from the original somatopleure (compare page 78), 

 consist of a mesodermic and an ectodermal layer. The ectoderm of the 

 amnion is a single layer of cuboidal cells placed on the side of the 

 membrane toward the embryo and away from the uterus. The ecto- 

 derm, c, of the chorion, on the contrary, is next the uterus. Hence it will 

 be noticed that the mesodermic layers of the amnion and chorion are 

 adjacent. Both membranes are quite thin. The decidua is a relatively 

 voluminous membrane containing blood-vessels, u, which for the sake of dis- 

 tinctness have been filled in with black in the drawing. It also contains a series 



