308 S. Vincent, 



the functional activity of the organs in the different species according 

 to their different habits of life, but more than this one cannot at present 

 affirm. The point which I wish to emphasise here is the marked and 

 uinversal distinction between the cortex and the medulla. This is 

 obvious enough without the application of any reagents, but can be 

 beautifully shewn by placing the gland, after being cut across, in a 

 solution of bichromate of potassium for a time, when the medulla 

 always becomes dark brown. As has been stated above for other 

 vertebrates, various staining re-agents mark the distinction quite well 

 for histological examination. Thus, if the gland has been hardened 

 in alcohol and stained with picro-carmine, the cortex has the proto- 

 plasm of its cells stained yellow anc^Vthe nuclei red, but the medullary 

 cells are scarcely touched by the picric stain. The same applies to 

 eosin and safranin. Thus the medullary protoplasm appears to stain 

 deeply with nuclear stains, but faintly with general stains. 



Medulla. In Mammals the evolution of the medullary gland has 

 become completed. There is little or no trace in its structure of 

 anything which would make us suspect its nervous origin. We find 

 certainly an abundance of nerve-cells in the medulla of some animals, 

 but, so far as I have been able to ascertain, there are none of those 

 transition forms which obtain so high up in the scale as birds. 



The cortex and medulla are always distinctly marked off from 

 each other, and liave every appearance of being what they really are, 

 two separate and distinct glands of different origin, and probably 

 totally different functions. There is in some species a septum of 

 connective tissue separating the two portions from one another. In 

 other cases the distinction is rendered obvious by tlie above-mentioned 

 staining reactions. 



The medullary cells are arranged in most Mammals in elongated 

 solid cords, in the form of a plexus. (PL XVIT. fig. 15), the inter- 

 spaces of the meshwork being occupied by a rich network of capillaries, 

 with here and there a large blood sinus. In man the arrangement is 

 practically that which has just been described except that the cords 

 are shorter, so that in section the cells of the medulla appear to be 

 arranged in rounded groups. 



