i^o HOWELL. 



EXPLANATION OF PLATE. 



Fig. I. a,b, c, d. Drawings of megakaryocytes, to show some of the variations in 

 structure of the nucleus. e,f. Megakaryocytes in which the nucleus stains diffusely 

 and fragments into smaller pieces, explained as degenerative changes. 



Fig. 2. Three megakaryocytes; two in the act of dividing; from a camera lucida 



sketch. • 



Fig. 3. Two megakaryocytes; division complete, but the cells still connected; 



from a camera lucida sketch. 



Fig. 4. Four cells from the developing marrow in a section of the femur of a foetal 

 cat 9 cms. long, stained with saffranin, and intended to illustrate the development 

 of a megakaryocyte from a marrow corpuscle. 



Fig. 5. Section of the liver of a cat embryo 2.7 cms. long, showing a mega- 

 karyocyte lying in a developing blood vessel, and surrounded by erythroblasts. 



Fig. 6. Section of the hind leg of the same embryo, to show a megakaryocyte 

 lying in a developing blood-vessel of the muscular tissue. On one side there is still 

 a solid cord of erythroblasts, with some nucleated red corpuscles; on the other the 

 blood plasma and fully formed nucleated red corpuscles lie in contact with t!he giant 

 cell. 



Fig. 7. Camera lucida sketch from the section of the femur of the foetal cat 9 cms. 

 to show the reticulum radiating from the megakaryocytes found in the marrow. 



Fig. 8. A megakaryocyte surrounded by its broad envelope of secreted material 

 from a preparation of the marrow of a young kitten, teased in a weak solution of 

 methyl green in normal salt. 



Fig. 9. The same cell, showing the vacuolation that takes place in the enveloping 

 substance. The vacuoles at first small, as on the under side of the cell, become larger, 

 until they form a structure resembling somewhat the reticulum shown in Fig. 7. The 

 sketches of the vacuolation were made at different times, and have been shown in 

 the same figure to indicate the gradual growth. 



Fig. 10. A megakaryocyte from a similar preparation, in which the action of the 

 reagent had gone so far before the cell was examined, that a number of vesicles 

 adhering to the cell was all that remained of the original envelope. 



