26 K. MITSUKURI. 



by him to be developed. These cords join the continuation 

 of the nervous mass (n, figs. 5 and 6) just at the point 

 where the cortex ceases. The cords seem to U7iite with each 

 other at one point, although soon separating again. Professor 

 Kolliker (loc. cit. p. 953) remarks that in the sixteen- 

 and seventeen-day embryo rabbits, the suprarenals of two 

 sides unite behind, while the front parts are separate. It 

 seems evident to me that he has not clearly distit)guished 

 between the cortical and medullary part. The cortical parts of 

 two sides certainly show no signs of uniting with each other at 

 any stage of development, while, if reference is made only 

 to the continuations of the medullary part, it is not only in 

 the sixteenth to seventeenth day, but at much later stages that 

 they are found uniting with each other. Of certain histo- 

 logical peculiarities of other cords I shall speak later on. 



The method of entrance of the medullary substance into 

 the suprarenal bodies may be stated briefly as follows : — The 

 peripheral sympathetic plexus, which is formed ventrally to 

 the aorta in the abdominal region, sends in processes into 

 the body of suprarenals at various points — the one at the 

 posterior end of the organ being by far the largest — and the 

 cells thus carried in become gradually transformed into the 

 cells of the medullary substance. 



In embryos of sixteen days, all the essential parts of the 

 suprarenals are already present, and henceforth the develop- 

 ment consists simply in their histological elaboration : — I 

 shall rapidly describe the successive stages until we come to 

 the twenty-sixth day, which, being the last I have observed, 

 I shall treat of somewhat minutely. On the eighteenth 

 day the suprarenals are already visible to the naked eye 

 as oval bodies on the inner side of the kidney, and substan- 

 tially resemble the adult bodies in regard to position, shape, 

 and symmetry. This stage is the earliest of which I have 

 embryos hardened in bichromate of potash. 



The medullary part takes already a slight brown staining, 

 and it is to be specially noted that the continuation of it 

 behind the cortical substance is also affected in the same 

 way. The cortical substance has increased considerably in 

 quantity, and the irregular cords of cells begin to assume a 

 more regular oval or polygonal form. In regard to the em- 

 bryos of the twentieth, twenty-second, and twenty-fourth days, 

 of which I have sections, there is nothing special to mention, 

 except that the suprarenals become gradually larger, that the 

 medullary and cortical substances increase accordingly, and 

 that the cell groups in the cortex become more and more defi- 



