-•">- M. IXAKA. 



To trnoo the on'o-in of the cortical snhstanco is in far-t extroniel}^ 

 difficult, as its cells are faintly distinguished from the other tissue 

 cells. The cortical hlastema in the mouse is tolerably v:e]] seen in 

 the early stage of the 12th day of gestation. The mesonephros in 

 the monse is very weakly developed. Only the aiiterior two or three 

 segmental tuhiiles actna]l3M-)pen to the Wolffian duct ; iolh^.wing these 

 ran be traced five or six blind tubules, vhicli lessen in size one after 

 another, until finally no tul)ular structure is seen beyond tlie 8th or 

 9th one, the cells being merely clustered in ])r(^per ])laces. The 

 supi'arenal blastema extends from about the middle of the anterior 

 two segmental tuljules to about tlie 6th or 7tli tubule. In ci'oss 

 section, it is large anteriorly and gradually lessens in size posteriorlv. 

 It is placed just at the angle of the mesentery (PI. XXX. figs. .") and n\ 

 occupying the space enclosed by the aorta and the cardinal vein on 

 the medial and dorsal side, and liy the mesonephrc^s and the genera- 

 tive organ on the lateral size. ^Fediallv the [blastema is distinctly 

 liounded by connective tissue cells. Where the S-shaped segmental 

 tul)ules are projected in medial direction, they approach the dorsal end 

 of the suprarenal blastema ; in other cases they are far removed from 

 the suprarenal. In no cases do the tubules send out cells medially. 

 The walls of the cardinal vein show no signs of proliferation. 

 ]>ranches of the vein to the suprarenal are not yet developed. 



The relation of the suprarenal blastema with the beginning of 

 the generative organ is interesting. These two blastemas are ]il;iced 

 side bv side, their anierioi- extremities reaching about the same level, 

 but posteriorly the generative blastema extends far beyond the 

 end of the suprarenal. The cell elements of the two are very similar, 

 consisting of large cells with large round nuclei, which are stained 

 slightlv deeper than those of the connective tissue cells. Ihit the 

 two blastemas are separated from each other in all places, except at 



