COLOURLESS CORPUSCLES. 1 3 



contain clear spaces or vacuoles, and it has a reticular structure. Each 

 pale corpuscle has one or more nuclei, which are difficult to see without 

 the aid of reagents. 



In the clear fluid in which the corpuscles are suspended, a network 

 of fine straight intercrossing filaments (fibrin) soon makes its appearance 

 (fig. 10, A). There are also to be seen a certain number of minute 

 round colourless discoid particles, either separate or collected into groups 

 or masses, which may be of considerable size. These are the elementary 

 particles or blood-tablets. Their meaning is not known. Fatty particles, 

 derived from the chyle, may also occur in the plasma. 



Development of blood-corpuscles. In the embryo, the first-formed 

 coloured blood-corpuscles are amoeboid nucleated cells, the protoplasm of 



FIG. 11. DEVELOPMENT OF BLOOD-VESSELS AND BLOOD-CORPUSCLES IN THE VASCULAR 

 AREA OF THE GUINEA-PIG. 



l>l, blood-corpuscles becoming free in the interior of a nucleated protoplasmic mass. 



which contains haemoglobin. These embryonic blood-corpuscles are 

 developed within cells of the mesoblast, which are united with one 

 another to form a protoplasmic network (fig. 11). The nuclei of the 

 cells multiply, and around some of them there occurs an aggregation of 

 coloured protoplasm. Finally the network becomes hollowed out by an 

 accumulation of fluid in the protoplasm, and thus are produced a num- 

 ber of capillary blood-vessels, and the coloured nucleated portions of 

 protoplasm are set free within them as the embryonic blood-corpuscles 

 (fig. 11, bl). 



In later embryonic life, nucleated coloured corpuscles disappear from 

 mammalian blood, and are replaced by the usual discoid corpuscles. 

 These are formed within certain cells of the connective tissue, a portion 

 of the substance of the cell becoming coloured by haemoglobin, and 

 separated into globular particles (fig. 12, a, b, c), which are gradually 

 moulded into disk-shaped red corpuscles. In the meantime the cells 



