10 THE ESSENTIALS OF HISTOLOGY 



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- tab lets. Their meaning is not known. 

 Fatty particles 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 



* 



\ 



F IG . 8. DEVELOPMENT OF BLOOD-VESSELS AND BLOOD-CORPUSCLES IN THE VASCULAR 

 AREA OF THE GUINEA-PIG. 



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



of which contains haemoglobin. These embryonic blood-corpuscles 

 are developed within cells of the mesoderm, which unite with one 

 another so as to form a protoplasmic network (fig. 8). The nuclei 

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

 of coloured protoplasm. Next the branched cells become hollowed 



FIG. 9. BLOOD- CORPUSCLES DEVELOPING WITHIN CONNECTIVE-TISSUE CELLS. 



h, a cell containing diffused haemoglobin ; h', globu'ar masses of coloured substance in the 

 protoplasm, within which also are numerous vacuoles ; h' 1 , a cell filled with coloured 

 globules. 



out by an accumulation of fluid in their protoplasm so as to form a 

 network of blood-vessels, and then the coloured nucleated portions 

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

 corpuscles (fig. 8, bl). 



