STRUCTUKE OF THE SPLEEN. ARTERIAL SHEATHS. 355 



to whether they are developed from the entire circumference of 

 the arterial sheath, or from only a definite point of it ; in the 

 former case, surrounding the artery to which they belong like a 

 ring ; in the latter, being situated eccentrically, or being only 

 laterally attached. 



The parenchyma of the Malpighian bodies is formed of cells 

 and a retiform intermediate substance ; the cells agree in their 

 characters with the lymph corpuscles of the several animals, 

 and they are constantly found in various stages of development, 

 some being smaller, with a single nucleus, and others larger, with 

 several nuclei. Like those of the splenic pulp, they are capa- 

 ble of executing amoeboid movements, and are usually more 

 densely crowded at the periphery of the Malpighian bodies 

 than at their centre. When treated with solution of carmine, 

 cceteris paribus, they become more intensely tinted than those 

 of the pulp, though it has not been hitherto determined 

 whether the deeper hue is the consequence of the presence of a 

 larger proportion of protoplasm capable of imbibing the colour, 

 or to a difference in the fluid by which the protoplasm is per- 

 meated. 



Associated with the cells is a delicate intermediate substance, 

 the periplast of Huxley. This forms a network around the 

 several cells or groups of cells, and when examined in the recent 

 state, consists of a pale, extremely finely granular, tenacious 

 material, which presents the form of delicate fibrils in pre- 

 parations hardened in chromic acid. At the periphery of the 

 Malpighian bodies the network becomes closer, the individual 

 fibrils present a greater similarity to ordinary connective tissue 

 fibrils, and the meshes become more elongated and narrow, 

 though without actually forming a continuous membrane, as was 

 first correctly demonstrated by Henle. 



PULP. The tissue of the splenic pulp is composed of cells 

 and of an intercellular substance. The former resemble the 

 lymph corpuscles of the animal, and constantly appear as small 

 uni-nucleated and larger multi-nucleated cells, furnishing evi- 

 dence of the occurrence of continuous processes of new forma- 

 tion. These become less deeply tinted with carmine than those 

 of the Malpighian bodies, which they, however, resemble in 



