182 W. F. R. WELDON. 



before the entrance of the blood-vessels, none of which are 

 to be seen in the section figured. The epithelium is much 

 more columnar than at a later stage, and is regularly one cell 

 thick on the outer side, while on the side undergoing invagina- 

 tion it is more or less regularly composed of two layers of cells ; 

 but at every point except one the whole glomerulus is bounded 

 by cells of a definitely epithelioid character, having no pro- 

 cesses, and showing no indication whatever of any tendency to 

 proliferation. At the inner margin, however, the case is 

 diff"erent; here the limiting cells are irregular in shape, and 

 can in no way be separated, by any sharp line of demarcation, 

 from the cells forming the mass (s. r. b.), which is seen to 

 be attached to the inner wall of the glomerulus. This mass 

 gives rise both to the connecting tubules between testis and 

 epididymis and to the cortical substance of the suprarenale. 

 At present it is seen to extend for a short distance dorsal- 

 wards, between the segmental tubule (s. t.) and the vena cava 

 [v.c), and then to bend rather sharply ventralwards towards 

 the generative ridge, the anterior end of which ( W. r.) is seen 

 in the section. As a contrast to the continuity between the 

 cell mass in question and the cells bounding the cavity of the 

 glomerulus I would especially call attention to the distinctness 

 of the line of demarcation between it and the endothelium of 

 the vena cava, at the point where the two are in contact — a 

 distinctness which, persisting, as we shall see it to do, through 

 all stages of the development of the suprarenal blastema, ren- 

 ders it extremely difficult to believe that the endothelium is in 

 a state of proliferation, or that there is any real connection 

 between it and the suprarenal blastema. 



The small blood-vessel {b. v.) which is seen in the figure 

 is also perfectly sharply separated from the adjacent tissues. 



The section represented in fig. 2, from an embryo about 

 4"5 mm. long, with twenty-four protovertebrae, shows a further 

 advance in the development of the suprarenal blastema and its 

 associated glomerulus. The section, which passes through the 

 entrance of a segmental tube into the glomerulus, shows the 

 completion of the invagination, and the entrance of blood- 



