170 VICTOR E. EMMEL 



dem die Neigung Scheiben von bestimmter Form zu bilden, auch 

 in seinen kleinsten Partikelchen innewohnt;" (cf. also Erlich and 

 Lazarus '09, p. 67-68, and Weidenreich '03, p. 47-55). 



Not all the plastids, however, have this biconcave-disc or cup 

 shape. As a rule the smallest and not infrequently even the 

 largest ones are more or less spherical (figs. 27, 28, 8 6), as may be 

 positively ascertained by mechanically rotating the fresh unfixed 

 corpuscles. In this respect they correspond with many of the 

 newly formed plastids observed in the cultures. It is of interest 

 also to note that in the human embryo 'Hhe early human plastids 

 do not have the characteristic form of the definitive corpuscle, but 

 retain the spherical shape" (Minot '12, p. 509). 



Finally, a more or less spherical plastid is occasionally found 

 having a single fine hair-like process (fig. 8) . This process,which 

 seems unquestionably a part of the cell cytoplasm, drawn out 

 in this attenuated form, closely resembles the similar processes 

 which were occasionally observed to arise in the cultures, where in 

 an as yet uncompleted cytoplasmic constriction the intervening cy- 

 toplasm had become drawn out into a fine, almost invisible thread 

 (figs. 13, 20; cf. also p. 138). It seems difficult to escape the con- 

 clusion that these cytoplasmic processes in the circulating plas- 

 tids have also arisen in connection with a process similar to that 

 observed in vitro. 



d. Erythrocytic 7iuclei after plastid formation 



Free erythrocytic nuclei deficient in surrounding cytoplasm 

 have of course long been recognized and their presence in the em- 

 bryonic circulation advanced as evidence for the enucleation of 

 the erythroblast by a process of nuclear extrusion. In view of 

 the results of the present study, it may be questioned, however, 

 whether the latter conclusion follows necessarily. In the first 

 place, it will be recalled that in certain cases cytoplasmic constric- 

 tions were observed in the cultures in which the process took 

 place in such a manner as to leave a practically if not entirely 

 cytoplasm-free nucleus. Second, instances were noted in which 

 the cytoplasm surrounding the nucleus remaining after a com- 



