CHAPTER IX. 

 BLOOD-GLANDS AND DUCTLESS GLANDS. 



THE lymphoid glands pertaining to the lymphatic system 

 (lymphatic glands, tonsils, thymus, solitary and agminate 

 glands, etc.), are described elsewhere. 



Other structures, "blood-glands," bear the same relation to 

 the blood-stream that lymphatic glands do to the lymph stream. 



Of these the chief representative is the spleen, an important 

 gland partaking somewhat of the lymphoid type. In some 

 mammals other blood-glands occur, the " haemal glands." 

 Bone-marrow, in structure and function, forms a sort of u blood- 

 gland." Of similar nature, perhaps, are the small coccygeal 

 and carotid glands. 



The active ductless glands of the secretory or epithelial 

 type are the thyroid, parathyroid, adrenal, and pituitary bod- 

 ies ; besides these are the ovary (which is. of unique type), the 

 rudimentary pineal body, and certain atrophic foatal structures 

 about the genital organs, as the paradidymis and parovarium. 



The functions of all these structures are more or less obscure, 

 but (especially if the theory of internal secretion is true) they 

 may be considered as probably belonging, in common, to the 

 haemapoietic (blood-forming) and hsemolytic (blood-destroying, 

 blood -purifying) system, contributing corpuscular and chemi- 

 cal constituents to the blood or removing from it effete 

 materials. 



The Spleen. 



General structure : The spleen (Fig. 43) consists of a pulpy 

 parenchyma supported in a reticular sustentacular tissue ; 

 contains numerous lymphoid follicles (Malpighian corpuscles), 

 and is freely supplied with bloodvessels opening directly into 

 the reticular spaces. The outermost covering of the spleen 

 is formed by the peritoneum. 



104 



