374 



BLOOD-VESSELS. 



reddish globules, which are now becoming disk-shaped (&), are found. Finally the 

 cavity extends through the cell-processes into those of neighbouring cells and into 

 those sent out from pre-existing capillaries (fig. 434, c), but a more or less extensive 



Fig. 433. COMMENCING DEVELOPMENT OF ANGIOBLASTIC CONNECTIVE TISSUE CELLS INTO BLOOD-VESSELS. 



FROM THE SUBCUTANEOUS TISSUE OF THE NEW-BORN RAT. (E. A. S.) 



h, a cell containing haemoglobin in a diffused form in the protoplasm ; h', one containing coloured 

 globules of varying size, and vacuoles ; h", a cell filled with coloured globules of nearly uniform size ; 

 /, /', developing fat cells. 



Fig. 434. FURTHER DEVELOPMENT OP CONNECTIVE TISSUE CELLS INTO CAPILLARY BLOOD-VESSELS. 



(E. A. S.) 



a, an elongated cell with a cavity in its protoplasm occupied by fluid and by blood-corpuscles which 

 are still globular ; b, a hollow cell the nucleus of which has multiplied. The new nuclei are arranged 

 around the wall of the cavity, the corpuscles in which have now become discoid ; c, shows the mode of 

 union of a " hasmapoietic " cell, which in this instance contains only one corpuscle, with the prolonga- 

 tion (bl) of a previously existing vessel, a, and c, from the new-born rat ; b, from the foetal sheep. 



Fig. 435. ISOLATED CAPILLARY NETWORK FORMED BY THE JUNCTION OF SEVERAL HOLLOWED-OUT 



CELLS, AND CONTAINING COLOURED BLOOD-CORPUSCLES IN A CLEAR FLUID. 



c, a hollow cell the cavity of which does not yet communicate with the network ; p, p, pointed cell- 

 processes, extending in different directions for union with neighbouring capillaries. 



capillary network is often formed long before the connection with the rest of the 

 vascular system is established (fig. 435). Young capillaries do not exhibit the well- 

 known lines when treated with nitrate of silver, for the differentiation of the hollowed 



