6S ON THE SUPRA-RENAL, THYMUS, AND THYROID BODIES. 



siipra-renal capsules, the thymus, and thyroid, retain through- 

 out their existence the orioinal texture of the blastoderma. 



Proceeding therefore in the order of formation as well as 

 of position from the Wolffian body, I shall state very briefly 

 what I have observed concerning the mode of development of 

 the supra-renal capsules, thymus, and thyroid. 



In the embryo of the sheep, in which the branchial clefts 

 are still quite open, the omphalo-mesenteric vessels well 

 developed, the liver consisting of an equal-sized lobe on each 

 side of the intestinal tube, the Wolffian bodies well formed, 

 the allantois beginning to protrude from the abdomen, and 

 the umbilical vessels already apparent, there may be seen 

 between the internal anterior part of the Wolffian bodies and 

 the aorta at the origin of the omphalo-mesenteric arteries, and 

 also around the omphalo-mesenteric vein, where that vessel is 

 passing forward into the liver, a mass of blastema spread over 

 the internal surface of the fore-part of the Wolffian body, and 

 arranged in one or more masses between that gland and the 

 aorta. 



In embryos rather more advanced, these masses of blastema 

 become less distinct, apparently from their increased biilk 

 causing them to be applied more uniformly over the anterior 

 extremities of the Wolffian bodies. They may always be 

 detected by their whiter appearance, and by being destitute 

 of the cross-markings produced by the ducts of the Wolffian 

 glands. 



It is not till the testes, ovaries, and kidneys have appeared, 

 that the supra-renal capsules are recognised as distinct organs ; 

 and their progress after this period need not be considered 

 further at present. 



The cardinal veins of Eathke pass forward along the pos- 

 terior and lateral part of the Wolffian bodies ; after passing 

 beyond the blunt anterior extremities of these bodies, each 

 vein carries with it, or is covered by a thin layer of the bias- 



