LYJMPHATIC ORGANS 179 



Large pJiagocytes containing blood pigment and disintegrating red 

 blood cells are found in both forms of haemolymph nodes, but are 

 most numerous in the splenolymph type. In nodes which have a 

 brownish color when fresh, these phagocytes frequently almost com- 

 pletely fdl the sinuses. 



Further classification of haemolymph nodes has been attempted, 

 but is unsatisfactory, owing to the large number of transitional forms. 

 Thus many nodes arc transitional in structure betwen the hcemo- 

 lymph node and the ordinary lymph node, between the splenolymph 

 node and the marrowlymph node, and between the splenolymph 

 node and the spleen. 



Under normal conditions the haemolymph nodes appear to be 

 concerned mainly in the destruction of red blood cells; possibly also 

 in the formation of leucocytes. Under certain pathological con- 

 ditions they probably become centres for the formation of red blood 

 cells. 



Blood-vessels. — An artery or arteries enter the node at the hilum, 

 and break up within the node into small branches, which communi- 

 cate with the sinuses where the blood comes into intimate association 

 with the lymphoid tissue. From the sinuses the blood passes into 

 veins, which leave the organ either at the hilum or at some other 

 point on the periphery. The course which the blood takes in pass- 

 ing through the haemolymph node is thus apparently similar to that 

 taken by the lymph in passing through the ordinary lymph node. 



The relation of the haemolymph node to the lymphatic system is 

 not known, and like ignorance exists as to its innervation. 



The development of the haemolymph nodes is probably much the same as 

 that of the lymph nodes, except for the relation of the latter to the lymphatic 

 vessels, the sinuses of the haemolymph nodes being developed from blood-vessels. 



TECHNIC 



Same as for lymph nodes (technic i, p. 176). The nodes are found in greatest 

 numbers in the prevertebral tissue, and are often difficult to recognize. Fixing 

 the tissues in s-per-cent. formalin aids in their recognition as it darkens the nodes 

 while bleaching the rest of the tissues. 



The Thymus 



The thymus is an organ of foetal and early extra-uterine life; 

 reaching in man its greatest development at the end of the second 

 year. After this age it undergoes a slow retrograde change into fat 



