The Structure and Functions of the ha?molymph Glands and Spleen. 25 



called sinus, with the endothelium lining certain arteries and veins 

 entering the hilus of the gland (pi. I. fig. 5). Furthermore the endo- 

 thelial walls of the capillaries, leading from the sinus into the adenoid 

 tissue, is also directly continuous with the lining of the sinus itself 

 (pi. I. fig. 5 e. c c). 



The advantages derived from the breaking up of the sinuses by 

 the reticulum are many. In addition to forming a support for the 

 lymphoid tissue, the reticulum retards the velocity of the blood stream 

 by increasing the resistance; also the phagocytes are enabled to retain 

 their position, and are not swept into a heap in one portion of the sinus. 

 Furthermore, if the phagocytes derive their origin from endothelium 

 cells, as I believe to be largely the case, the opportunity of multi- 

 plication is increased proportionally with the increased area of endo- 

 thelium. These conditions all facilitate the process of Phagocytosis. 



The endothelium seems, from an examination of silver nitrate 

 preparations of capsule (pi II. fig. 14), to have much the same ap- 

 pearance in this situation as that covering the inner wall of blood 

 vessels generally. The particular cells lining the reticulum seem to 

 be more branching however, and are probably more irregular, an 

 adaptation to the irregular fibres which they encase. 



2. Differences in the histological details betiueefi the glands of 



different animals. 

 Frimâtes. The microscopical characteristics of hsemolymph glands 

 in man and monhey have been examined. In both these species 

 "haemal" glands occur. The peripheral sinus is small or disconnected, 

 the trabeculae weak; but the central sinuses are numerous and break 

 up the lymphoid tissue considerably. Germ centres are scarce, though 

 phagocytosis is frequently observed. 



Ungulates. The trabeculae in the haemal glands of the ox 

 are strong and numerous; the peripheral sinus is often small, but 

 the central blood spaces are abundant. Germ centres are scarce and 

 pliagocytosis is rarely noticed. In the sheexJ, the sinuses are much 

 larger, particularly the peripheral; the trabeculae vary in strength 

 with the size of the gland; the reticulum is fairly dense, as is always 



