160 VICTOR E. EMMEL 



assumed the appearance shown in the camera drawing (fig. 19, h). 

 By 11.47 the plastid had attained a cup shape (fig. 19, 1). The ob- 

 servations which were continued until one o'clock were made 

 under especially fortunate circumstances through the fact that 

 the corpuscle in question was slowly undergoing a rotation in 

 position. During the latter part of the observations the plastid 

 thus came to occupy a position with the opening of the cup turned 

 directly toward the observer (fig. 19, m). It will also be noticed 

 that in the drawing at 11.06 the appearance of the corpuscle is 

 suggestive of changes preparatory to a division into two parts, 

 but inasmuch as the plastid was slowly turning over in the culture 

 apparently what was seen at this stage was a profile view of a 

 biconcave disc, which in the further progress of the turning next 

 presented the circular outline shown in figure 19, ^. Consequently 

 in this case it appears that the newly formed plastid assumed 

 first a flattened or disc shape before becoming cup or bell-shaped. 

 It is of interest to note that the form changes just described oc- 

 curred in the homoplastic culture, a fact which suggests that the 

 character of the plasma may be a factor in determining the defini- 

 tive form of the non-nucleated corpuscle (cf. p. 146). Occasion- 

 ally, in the final stages of the constriction process, the cytoplasm 

 of the dividing erythroblast may be drawn out in such a manner 

 that with the completion of the constriction, the plastid, in- 

 stead of having the usually smooth contour of the newly formed 

 corpuscle, may be modified in form by the presence of a slender 

 cytoplasmic process persisting for a time in the region of final 

 separation from the parent cell (figs. 20, 17 and 1?.) 



3. CRITICAL DISCUSSION OF THE CULTURES AND CYTOPLASMIC 



CONSTRICTIONS 



In determining to what extent we are to regard as normal or 

 abnormal the behavior of the erythrocytes as observed in the 

 cultures, it becomes necessary to consider critically the conditions 

 under which these phenomena occurred, especially in view of the 

 well known fact that blood cells are normally and functionally 

 very sensitive in their reaction to environment. 



