'262 DR A. J. WHITING ON THE 



an intercellular substance of white or pearly appearance, which, after injection of the 

 spleen through the artery with silver nitrate solution, appears as a brown network, in 

 each mesh of which is a lymphoid cell. This network differs, therefore, from the adenoid 

 reticulum in being regular in size of mesh, and in being equally distinct at all parts of 

 the follicle. 



The adenoid sheath of the splenic arteries does not show any nodular swellings in 

 the fish, amphibians, or reptiles, nor in some birds. In the Cod, after the splenic 

 arteries have become somewhat diminished in size, while they are still accompanied by 

 the branches of the splenic vein, their thick fibrous coat becomes infiltrated with lym- 

 phoid cells. Except around the largest arterial branches, the matrix of this coat is not 

 strongly fibrous, but resembles very fine areolar tissue or mucous tissue. The lymphoid 

 cells are small, sparse, and stain deeply with hasmatoxylin. Among them red blood- 

 corpuscles are occasionally seen, indicating the presence of capillaries. The artery 

 with its adenoid sheath, together with the vein, and nerve trunks if present, are 

 surrounded by the hilar sheath, at the periphery of which a few muscle fibre cells 

 are seen. 



In the Skate there are groups of cells in relation with the walls of the splenic arteries. 

 Each group is nodular and not unlike the splenic follicle of the higher vertebrate, with 

 part at least of which it is probably homologous. They are conspicuous from their 

 reddish-brown colour, and, while some are plainly connected with the arterial wall, 

 others, which are cut at one side of the artery, appear isolated. The cells vary 

 considerably in size — the smallest are about the size of an average lymphoid cell, and 

 the largest are five or six times larger. The larger cells are each situated in a cell- 

 space, and contain one or two nuclei imbedded in reddish-brown granular protoplasm, 

 while the smaller consist of a single spherical nucleus surrounded by a mere rim of 

 protoplasm. Many of the nuclei show evidence of division. The cells appear to be 

 arranged in columns. Surrounding; each nodule is a belt of fibrous tissue derived 

 from the hilar sheath, and outside that is a zone of lymphoid cells which fades away 

 into the surrounding pulp. 



In the spleen of the Frog there is a grouping of lymphoid cells around the artery, 

 without any localised accumulation. Loosely arranged clusters of cells are especially 

 noticeable immediately under the capsule, most, if not all, of which are sections of the 

 adenoid sheath. There is apparently no peripheral zone of fibrous tissue ; but among 

 the cells were seen coloured blood-corpuscles contained within capillaries. 



In the spleen of the Tortoise the pulp and the adenoid tissue are nearly equal in 

 amount : the latter is more abundant near the capsule, the former near the centre. The 

 lymphoid tissue follows the course of the arteries in very broad bands, and nowhere 

 shows localised accumulation. Not the arteries alone, but also the veins are surrounded 

 by adenoid tissue as in the spleen of the skate. The artery while of considerable calibre 

 is closely surrounded by a thin layer of very delicate fibrous tissue, outside which is a 

 comparatively thick layer of adenoid tissue. As the artery becomes smaller the adenoid 



