ERYTHROBLASTS IN THE PIG EMBRYO 157 



They were observed more frequently on the second day than dur- 

 ing the first half-day. Their behavior may possibly be comparable 

 in this respect with the similar behavior described by Burrows, 

 Carrel and others in the culture of various tissues in which the 

 processes of growth in the tissue cells were observed to be less 

 evident during the earlier than the later stages of the culture. 

 That the present cytoplasmic constriction of the erythroblast 

 may, however, take place as soon as the cultures are made, is 

 illustrated in the blood of a 30 mm. pig, Experiment 43, h. This 

 culture was examined immediately after the completion of the 

 preparation of several cultures included in the experiment, the 

 technique for which had occupied approximately one hour's time. 

 As soon as examined, several erythroblasts in the culture were ob- 

 served to be at stages of activity indicative of subsequent cyto- 

 plasmic constriction. One of these cells was selected for con- 

 tinuous observation, the results of which are recorded in figure 13. 

 Third, as to the size and other characteristics of the 7iucleated 

 remainder of the parent erythroblast. In the present observations 

 the amount of cytoplasm remaining associated with the nucleus 

 corresponded more frequently to that shown in figures 13 to 17. 

 The quantity of cytoplasm may, however, vary consideral'ly, 

 so that whereas the amount present may, on the one hand, be 

 occasionally even more than that shown in these figures, on the 

 other hand, it may be reduced to a mere rim of cytoplasm or ap- 

 pear practically, if not entirely absent, especially where the cyto- 

 plasmic constriction occurred close to the nucleus (figs. 18 and 20) . 

 Usually the nucleus is small and compact in structure. In some 

 cases the lighter appearance of the cytoplasm as seen in the cul- 

 tures, suggested that this nucleated remainder is possibly not as 

 rich in hemoglobin as the non-nucleated plastid, although this may 

 possibly be in part due to a thinner and consequently more trans- 

 parent disc of cytoplasm about the nucleus. After the constric- 

 tion, the nucleated remainder of the cell may assume an apparently 

 quiet condition and manifest no further evidence of change during 

 4 period of several hours observation. In other cases the cell body 

 may slowly extend more or less blunt, rounded cytoplasmic proc- 

 esses which may then again be retracted. In some instances 



