156 VICTOR E. EMMEL 



containing element or plastid. During the remainder of the period 

 of observation these two parts became more widely separated but 

 neither manifested any further changes (stages e-i), both now 

 apparently assuming a quiescent condition at least as far as 

 indicated by any visual evidence of cytoplasmic activity. In the 

 present case it will be observed that the two bodies are approxi- 

 mately equal in diameter. In the nucleated portion, the nucleus, 

 which has maintained a constant appearance in structure, size 

 and form throughout the process, is surrounded by a considerable 

 amount of cytoplasm; the cell body is slightly irregular in form 

 with the cytoplasm accumulated somewhat more upon one side 

 of the nucleus than the other. The non-nucleated portion, or 

 plastid, as it may now be conveniently designated, presented 

 a smooth, rounded contour, appeared to be homogeneous in struc- 

 ture, and in both size and amount of hemoglobin could not be dis- 

 tinguished from the average plastids, or non-nucleated erythro- 

 cytes, surrounding it in the microscopic field (cf. fig. 13, stage t). 



Having described a typical case of the origin of plastids by this 

 method, variations in the process as observed in the autoplastic 

 cultures may now be considered. 



First, as to the time involved in the constriction process. In the 

 instance just described it will be noted that an interval of about 

 twenty minutes elapsed between the time of the first observation 

 and the completion of the cytoplasmic constriction. This time 

 varies, however, from a few minutes, or even seconds, to thirty 

 minutes or longer, (figs. 13 to 20), depending obviously, in part at 

 least, upon the stage of the process at which the observations were 

 begun. After some experience the observer tends to become more 

 proficient in selecting erythroblasts at stages of activity which are 

 usually soon followed by a completion of the constriction with- 

 in a few moments, although not infrequently the characteristic 

 changes preliminary to a constriction may be observed for several 

 hours without the occurrence of any marked progress, the ceU 

 sometimes even becoming apparently quiescent again. 



Second, as to the time of occurrence in the cultures. Typical cyto- , 

 plasmic constrictions of the type just described may be found in 

 good cultures at any time during the first two or three days. 



