ox SUPRAKEXAL BODIES IX THE MOUSE, 217 



one month old. In thtse specimens, the two substances of the 

 suprarenal bodies are already well marked. In cross sections, the 

 organ is elliptical, consisting of two concentric zones (PI. XXXI. tig. 

 21); the inner central zone (med.) stnins somewhat less than the outer 

 zone (cor.). Under a high power, the central zone is found to be 

 composed of irreü;ular cord-like cell-a^'o-reo-ates. each of which is 



i O Co o 



bounded by strong connective tissue fibres. The cell-protoplasm is 

 faintly stained ; the nuclei are large (6 U- on an average) and slightly 

 granular. The nuclei of the cells of the outer zone are smaller in size 

 (5 /z.) and highly granular. Their cells are smaller than those of 

 the central z(3ne ; this is especially the case in the middle portion of 

 the outer zone where the cell-protoplasm is stained deeper than in 

 any other part, so that the outer zone is subdivided into these minor 

 concentric zones. But these three zones gradually merge one 

 into another without presenting any distinct limit. The transition 

 from the <3uter (cor.) to the central zone (med.), on the other hand, is 

 very sudden ; the limiting line is distinct and tolerably even, forming 

 an elli[)tical outline. Evidently the central zone is the medulla, and 

 the outer the cortex. 



Turning now to the mouse ten days old (PI. XXXI. fig, IS), a 

 considerable difierence is observed in the structure of the medulla. 

 The medullary substance (med.) projects irregularly into the cortex 

 (cor.), and the boundary is not yet even, though its elliptictd outline 

 can already be made out. The cells and nuclei of the medulla are 

 stained deeper than befjre, so that the distinction of it from the c(.)rtex 

 is obscure in some parts where the farmer projects int(j the latter. The 

 difficulty is further increased by the fact that the cord-like arrangement 

 of the medulla is as yet very weakly developed, and the respective 

 sizes of the nuclei in the two substances are approximately equal. 

 Put tracing carefidly the nnirgin of the medulla, we can tind here and 



