2IO 



HISTOLOGY 



blood corpuscles fragment in passing through it, and are removed from the 

 circulation by phagocytic cells, which in consequence become pigmented. 

 The eosinophilic cells which are found in haemolymph glands have been 

 explained as due to the ingestion of haemoglobin products, but it has 

 been questioned whether these cells are more abundant than in ordinary 

 lymph glands. A second function of the haemolymph glands, depending 

 upon the lymphoid tissue around their arteries, is the production of 

 lymphocytes which may enter the blood vessels directly. 



According to von Schumacher (Arch. f. mikr. Anat., 1912, vol. 81, pp. 92-150) the 

 haemolymph glands begin their development like ordinary lymph glands, but after the 

 formation of the peripheral sinus, the connections with afferent and efferent lymphatic 

 vessels are lost. He finds various intermediate forms between the lymph and haemo- 

 lymph glands, depending upon the extent of atrophy of the lymphatic connections, and 

 the extent to which blood escapes from the intraglandular vessels. After accidents 

 accompanied by extravasations of blood, the sinuses of ordinary lymph glands may be- 

 come filled with red corpuscles, conveyed to them by the afferent lymphatic vessels. 

 Such glands differ obviously from the true haemolymph glands, which structurally and 

 functionally are intermediate between lymph glands and the spleen. 



SPLEEN. 



The spleen, being five or six inches long and four inches wide, is much 

 the largest organ of the lymph gland series. It is the first of them to de- 

 velop, appearing in rabbits of 14 days (10 mm.) as a condensation of the 

 mesenchyma in the dorsal mesentery of the stomach. At this stage the 



art 



FIG. 198. DIAGRAM OF A HAMOLYMPH GLAND. A; AND OF A PART OF THE SPLEEN, B. 

 The arteries are shown as slender lines (art.) and the veins as heavy ones (v.); c., capsule; b. s., blood 

 sinus, corresponding with the splenic pulp, p.; s . n., secondary nodule; sp. n., splenic nodule; tr., 

 trabecula. 



only lymphatic vessels in the embryo are those near the jugular vein. 

 Lymph glands are not indicated until six days later. The blood vessels 

 enter the spleen at its hilus and branch freely. In early stages they form 

 an ordinary capillary plexus, but subsequently their walls become so per- 

 vious that most of the blood escapes into the reticular tissue in passing 



