500 



VETERINARY PHYSIOLOGY 



called hsemolymph glands (fig. 205). They are intermediate 

 between lymphatic glands and the spleen. 



3. Bone Marrow (fig. 204). — Young leucocytes or leuco- 

 blasts, in the condition of mitosis, are abundant in this tissue, 

 often in patches, the leucoblastic areas, and they pass away 

 in the blood stream. They are of all varieties. In digestion 

 leucocytosis and in certain pathological conditions the for- 

 mation of these cells is increased and a leucocytosis results. 





Fig. 204. — Section of Red Marrow of Bone, a, lymphocyte ; h, fat cell ; c, 

 erythroblast ; d, giant cell ; e, erythrocyte ; /, erythi'oblast in mitosis ; 

 g, neutrophil myelocj'te ; /;, eosinophil mj-elocyte ; k, eosinophil 

 leucocyte ; I, polymorpho-nuclear leucocyte. 



II. Erythrocytes. — In the embryo, these cells seem to be 

 formed by a process of budding from the mesoderm cells, 

 which become vacuolated to form the primitive blood-vessels. 

 The primitive red cells are larger than those of later life, and 

 they have a very distinct nucleus. In extra-uterine life they 

 occur in the blood as megaloblast.-i in some blood diseases. 



A new set of nucleated red cells next develops in the liver, 

 and later in the spleen and bone marrow. They are smaller 

 than the megaloblasts, and they are known as normoblasts 

 when they appear in the blood in extra-uterine life, as they 



