ON THE SUPRA-RENAL, THYMUS, AND THYROID BODIES. 77 



that performed by the blastoderma, whatever the exact nature 

 of that function may be. 



I have therefore been led to consider tlie supra-renal 

 capsules, the thymus, and thyroid, as organs essentially similar 

 in structure ; as developments of the remains of the blasto- 

 derma, being" formed of a continuous portion of that part 

 situated along each side of the spine, from the "Wolffian bodies 

 to the base of the cranium, the supra-renal capsules being de- 

 veloped in connection witli the omphalo-mesenteric vessels, 

 the thpuus to the jugular and cardinal veins, and ductus 

 Cuvieri ; and the thyroid to the anastomosing branches of the 

 first and second aortic arches, as organs performing functions, 

 whatever these may be, analogous to those of the blastoderma, 

 differing from them only in this, that the blastoderma not only 

 elaborates nourishment for the embryo, but absorbs it also 

 from without — that is, from the yelk ; whereas the three organs 

 in question only elaborate the matter which has already been 

 absorbed by the other parts, and is now circulating in the 

 vessels of the more perfect in dividual 



