DESCRIPTION OP PLATES VI— IX— continued. 



PLATE IX. 



Figs. 43 to 48 are magnified 265 diameters, figs. 49 and 53, 385 diameters, 

 fig. 51 magnified 18 diameters, and fig. 52, 15 diameters. 



Pigs. 43, 44, and 45 transverse sections througli about the centre of the 

 medullary groove of embryos at different stages of growth. Pig. 43 is a section 

 through the embryo drawn in fig. 13. They exhibit the gradual deepening of 

 the medullary groove, the isolation of the axial hypoblast from the lateral 

 mesoblast, and the reduction in bulk of the former. 



Pigs. 46 and 47. — Transverse sections through the embryo drawn in fig. 14. 



Fig. 46 is through the tongue-shaped dark line projecting forward from the 

 anterior end of the medullary groove. 



Fig. 47. — A section through the medullary groove in a region similar to 

 that from which the sections drawn in figs. 43 to 45 were taken. 



Fig. 48. — Transverse section through the region anterior to the medullary 

 groove of the same embryo from which fig. 45 is taken. 



Fig. 49. — Transverse section through the embryonic area of a rabbit's ovum 

 six days four hours old. The sections throughout are similar to the one here 

 figured, and show the cells of the outer layer (t. c), Rauber's Decksellen, 

 becoming incorporated with the cells of the inner mass, the two together 

 forming the epiblast of the embryo. 



Fig. 50. — Diagrammatic longitudinal section through the middle line of the 

 hind end of an embryo similar to that drawn in fig. 14, The medullary groove 

 has not as yet enclosed the neurenteric canal. The latter is continuous from 

 the epiblast through the mesoblast to the hypoblast, and opens dorsally and 

 ventrally through the former and latter layers. At p. skJ the three layers are 

 united, behind and in front the hypoblast is free. The amnion is formed over 

 the hind end of the area. 



Fig. 51. — Transverse section through the uterus of the mole from which 

 the vesicle drawn in fig. 8 was obtained. The section passes through the 

 region in which the vesicle was placed. The widely opened mouths of the 

 uterine glands into which the papillae of the vesicle projected are seen in con- 

 nection with the stems of the glands. The uterine epithelium is represented 

 in the drawing slightly too thick, and the width of the mouth of the glands to 

 which the reference lines ut. gls', point is somewhat exaggerated. 



Fig. 52. — A piece of uterine epithelium torn away from the uterus. The 

 papillae are hollow, and are formed of the epithelium lining the mouths of the 

 glands, which is continuous with the epithelium of the uterus. The uterus 

 from which this was obtained is the same as that from which the section, fig. 

 51, was made. 



Fig. 53. — Section of the wall of a blastodermic vesicle (at the primitive 

 streak stage) at the non-embryonic pole, and of the uterine epithelium to 

 which it was attached. 



