126 HOWELL. [Vol. IV. 



ceptive. I was not able to obtain a sufficient number of clear 

 cases to convince me that this is a normal occurrence in the life 

 of these cells, though at the time I was convinced that their 

 most probable function was to form the erythroblasts or pro- 

 genitors of the nucleated red corpuscles ; indeed, I abandoned 

 the theory reluctantly because the evidence seemed to be 

 opposed to it, or at least did not support it. If we adopt the 

 compromise view that the giant cells furnish some of the 

 erythroblasts while others, and probably most of the others, 

 arise in a different way, then we could understand why in rapid 

 regeneration of the blood after bleeding it is so rare to find 

 giant cells in the act of producing erythroblasts. But it does 

 not seem probable, to me at least, that these cells should be 

 produced in one organ by two different methods. Neverthe- 

 less, the constant presence of megakaryocytes in the blood- 

 forming organs induces me to believe that they have some 

 function to perform in connection with the formation of blood. 

 This is rendered more probable by the fact that in the embryo, 

 at least, the megakaryocytes can be found in the newly forming 

 blood-vessels surrounded by developing blood corpuscles. I 

 have found this in sections of the liver of an embryo cat where, 

 as has been described in another paper, the nucleated red cor- 

 puscles and the erythroblasts lie in cords which are destined to 

 become the future blood-vessels of the liver. In some cases, 

 in fact, the cords may be seen to end in channels filled with 

 coagulated plasma and red corpuscles, with or without nuclei. 

 Now, in these cords of blood cells I have found the megakary- 

 ocytes, showing that they are connected in some way with the 

 blood (Fig. 5). In longitudinal sections of the hind leg of 

 the same embryo I have found developing blood-vessels lying 

 among the embryonic muscle fibres and in the blood-vessel 

 giant cells, — megakaryocyte, — as shown in Fig. 6. It is very 

 hard to understand what this cell is doing in such a place 

 if it is not connected with the production of either the formed 

 elements or of some of the chemical constituents of the blood. 

 As I have just said, I cannot find any corroborative evidence 

 for the first view, and am therefore inclined to look favorably 

 upon the second ; namely, that the function of the megakary- 

 ocyte is to manipulate, in some way, the material of the plasma 

 or lymph, forming some substance for the nourishment of the 



