ERYTHROBLASTS IN THE PIG EMBRYO 159 



between two cover glasses in such a way as to render it impossible 

 by artificial manipulation, to observe various sides of a given cor- 

 puscle/ In such cultures success was attained in observing sev- 

 eral cytoplasmic constrictions. The newly formed plastids which 

 under these conditions could be turned over at will, presented a 

 more or less rounded shape in all views. 



The question at once arises whether these plastids can be ob- 

 served in the cultures to undergo any further form changes, and 

 whether there is any evidence of a tendency toward the assumption 

 of the definite biconcave-disc or cup shape. The data bearing on 

 this question are derived from plastids kept under continuous 

 observation for varipus periods of time, some of them for two or 

 more hoiu-s. Usually immediately after its formation the plastid 

 appears somewhat unstable in form as indicated by varying de- 

 grees of departure from a rounded contour and readjustments to 

 the original shape (figs. 17,18). In some cases the plastid would at 

 once, or within a few minutes, assume a fixed and apparently 

 stable form, no further changes being discovered during the period 

 of observation (cf. figs. 14 to 16). In other instances, however, the 

 plastids tend to become flattened and centrally constricted. 

 Sometimes this constriction was observed to result in the subdi- 

 vision of the corpuscle into two parts, especially in what appeared 

 to be the more unfavorable cultures. That these changes may even 

 in cultures culminate in the assumption by the corpuscle of a cup 

 or bell shape is illustrated in figure 19 from a culture of the blood 

 of a 28 mm. pig embryo in the centrifuged plasma of a 52 mm. em- 

 bryo. The newly formed plastid in this instance became constricted 

 off from the parent erythroblast at 10.40 a.m., and appeared more 

 or less spherical in shape. Evidence of instability in form, how- 

 ever, soon became evident, and by 11.06 a.m. the corpuscle had 



■* After considerable experimentation the following method proved the most 

 satisfactory: the culture drop suspended on the under side of a rectangular cover 

 glass was carefully brought into contact with a second smaller cover glass. The 

 latter consisted of a thin circular disc about 12 mm. in diameter, one edge of which 

 had been slightly thickened or bent by heating. This light disc, when brought 

 into contact with the culture medium, was held in place by capillary attraction 

 while at the same time its thickened rim prevented compression of the enclosed 

 blood cells. These preparations were then placed over hollow ground slides and 

 sealed in the usual manner with vaseline. 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 16. NO. 2 



