278 James Homer Wright. 



the pseudopod was shown by serial sections. At the right lower corner of the 

 drawing are shown three blood platelets and a lymphocyte. The other small 

 cells in the vessel are leukocytes. 



Fig. 7. Megakaryocyte in the act of protruding a pseudopod through the wall 

 of a blood vessel into its lumen. At the extremity of the pseudopod three 

 platelets in process of development. Further down in the blood vessel four free 

 platelets. Vacuoles in cytoplasm and in some platelets. 



Fig. 8. Detached pseudopods projecting into a blood vessel and in process of 

 segmentation into platelets. Free platelets also shown. Vacuoles in cytoplasm 

 and in platelets. 



Fig. 9. A mass of cytoplasm of a megakaryocyte with platelets budding off 

 from it. Free platelets and different forms of white blood corpuscle also shown. 



Fig. 10. Detached pseudopods and blood platelets. One of the pseudopods 

 segmenting into blood platelets. 



Fig. 11. Same as fig. 10, except that one of the larger granular red masses is 

 in continuity with a giant cell not obvious in the section. 



Fig. 12. Megakaryocyte protruding a pseudopod into a blood vessel through an 

 opening in its wall, At the tip of the pseudopod two or three platelets in process 

 of development and two or three developed platelets. The arrangement of the 

 granules in rows is shown. 



Fig. 13. Megakaryocyte showing a platelet in process of pinching off from a 

 pseudopod protruding through the wall of a small blood channel. 



Fig. 14. Megakaryocyte extending two pseudopods into a blood vessel through 

 openings in its wall. A blood platelet pinching off from one of them. Two blood 

 platelets free. Vacuoles in the cytoplasm of the giant cell are shown. 



Fig. 15. Megakaryocyte with a blood platelet in process of budding off into a 

 small blood channel. Two other blood platelets in the lower part of the figure. 



Fig. 16. One of the forerunners of the megakaryocytes observed in the blood 

 of a young guinea pig embryo. This cell is apparently in process of development 

 out of an endothelial cell of a blood vessel. It still forms part of the endothelium 

 of the wall of the blood vessel and it clearly is a transformed endothelial cell. 



Fig. 17. One of the forerunners of the megakaryocytes in the blood of an early 

 guinea pig embryo in process of breaking up to form blood platelets. Free blood 

 platelets also are shown. 



Figs. 18-21. Spindle cells or thrombocytes of Batrachuceps aUenuatus and free 

 blood platelet-like corpuscles. Smear preparations stained by Wright's blood 

 stain. Various phases are shown in the process of pinching off portions of the 

 cytoplasm of the thrombocytes to form blood platelet-like corpuscles. The 

 thrombocyte in fig. 18 has lost nearly all its cytoplasm by the process of pinch- 

 ing off of platelet-like fragments. The yellow body in one of the cells in fig. 21 

 is a fragment of a red blood corpuscle that has been taken into itself by the cell. 

 Note the vacuoles in the platelet-like body in fig. 19 and in the pseudopods in 

 fig. 21. 



