78 



GENERAL PRINCIPLES OF ZOOLOGY 



arrange themselves parallel to the surfaces mentioned, two systems may be 

 distinguished in cross-section, the fundamental lamella; and the Haversian 

 lamellcc. The former are arranged parallel to the surface of the periosteum 

 and of the marrow-cavity and form a mantle of concentric layers around the 

 marrow-cavity. Into this groundwork the Haversian canals with their lamellae 

 enter, destroying and superseding the fundamental lamellae coming in their 

 way. The Haversian lamellae are concentrically arranged around the lumen 

 of the Haversian canals just as the fundamental lamellae are around the marrow- 

 cavity and beneath the periosteum. 



Formation of Bone. The stratification of bone is caused by its mode of 

 origin. Where the bone borders upon the Haversian canals, the marrow-cavity, 

 and the periosteum, there is transiently or permanently an epithelial-like layer 

 of cells, osteoblasts, which secrete the bone-substance on their surface, which, 

 as with all similar conditions, gives the substance a stratification. Certain cells 

 in the matrix participate in this secretion, and here give rise to the bone-cor- 

 puscles, which are distinguished from the cartilage-cells by their numerous 

 processes ramifying through the matrix. The processes of a bone-corpuscle 

 branch and unite with the neighboring cells through fusion of the processes, an 

 arrangement most beautifully seen in dried bone, because here the cavities and 

 the canals of the matrix are filled with air. In spongy bone the structure is 

 simplified since the Haversian canals with their lamellae, and often the stratifica- 

 tion of the ground lamellae, are lacking. Special modifications of bone are 

 found in the substance of fish scales and in the dentine or ivory of teeth. 



' o~6a 



Blood and Lymph, here treated in connection with the connective 

 tissues, are in reality not tissues at all, but nutritive fluids. Two kinds 



of nutritive fluids occur in the verte- 

 brates, red blood and the colorless, 

 weakly opalescent, or cloudy white 

 lymph. The blood of man and other 

 vertebrates consists of a fluid and the 

 organized constituents. The fluid or 

 blood- plasma is specially rich in proteids; 

 after the removal of the blood from the 

 blood-vessels a part of these separate by 

 coagulation and form the blood-clot, 

 made up of fibrin, leaving a fluid poor 

 in proteids, the blood-serum. The organ- 

 ized constituents, the blood-cells, are dis- 

 tinguished as red and white blood-cor- 

 puscles. The latter, the leucocytes, are 

 present in smaller numbers and have 



great similarity to the Amoebae; they are particles of protoplasm, con- 

 tain a nucleus, devour foreign bodies (for example, carmine granules 

 injected into the blood), and move in the 'amoeboid' manner by putting 

 out pseudopodia (fig. 46). 



FIG. 46 White blood-corpus- 

 cles a, of man; b, of crab (n, the 

 nucleus). 



