DESCRIPTION OF THE FIGURE8 OE PL. IV— VI 



Note. I had originally made a large number of camera drawings, under- 

 various magnifications, of the histology of the placenta; I also took a cer- 

 tain number of photographs. It was however found impracticable to repro- 

 duce either; the accompanying figures are accordingly copies of these drawings 

 and photographs, carefully traced from the originals. 



Fig. 1 — 11 are purely diagrammatic, although the relative proportions of 

 the various parts have been faithfully adhered to; figures 7 — 11 are copied 

 from photographs. 



The remaining figures are unavoidably diagrammatic to a certain extent; 

 but will, I hope, exhevit some of the characters of nuclei and cytoplasm. 



The originals of figures 1 — 6 were drawn with Zeiss obj. B. comp. oc. 

 4 x 100, those of figures 12—40 with Zeiss 2 mm. comp. oc. 4 X 600. The 

 magnification of the photographs from which figures 7 — 11 are copied was 

 thirty diameters. Figures 1 — 11 have all been reduced to two thirds; the 

 magnifications of the first six is therefore now about sixty-five, of the last 

 five about twenty diameters. 



LIST OF REFERENCE LETTERS. 



a. allantois; a.c. allantoic capillary; a. t. allantoidean trophoblast: cap. 

 capsularis; c.m. circular muscles; e.t. layer of flattened connective tissue 

 cells; d.y. distal wall of yolk-sac; emb. embryo; en. endothelium; ep. d. 

 epithelial débris; ex. extra-embryonic coelom; f.c. flattened cells; g. uterine 

 gland; l.m. longitudinal muscles; m.g.c. maternal glycogen cells; m.m. 

 mesometrium ; n.g. neck of gland; s.ep.o. subepithelial tissue of the om- 

 phaloidean region ; o.t. omphaloidean trophoblast; p. y. proximal wall of 

 yolk-sac; s. c. supporting cells; s. ep. subepithelial tissue; t. I. trophoblastic 

 lacuna; t.s. trophoblastic blood sinus; n.a. maternal artery; u.b.v. mater- 

 nal blood vessel ; u.e. uterine epithelium ; u.v. maternal vein: v.f.c. vacuo- 

 lated subsequently flattened cells; y.s. yolk-sac; y.si. yolk-sac sinus. 



In Figs. 1 — 11 the uterine tissues are shaded, the trophoblast is dotted, 

 the area vasculosa and allantoic capillaries black. 



Fig. 1. A strip through the uterus figured in Fig. 8. 



The lumen is still bounded in its uppermost part by a normal 

 columnar epithelium ; this passes lower down into a cubical epithe- 

 lium ; lower down still the epithelium has entirely disappeared from 

 the sides of the embryonic pit. Around this pit, and less clearly 



