ERYTHROBLASTS IN THE PIG EMBRYO 183 



stricting off parts of their cytoplasm and liberating them into the 

 vascular system. 



The occurrence of this process in these three types of cells is 

 more than ordinarily interesting on account of their apparently 

 close relationship genetically. Weidenreich ('11) has already 

 called attention to this comparison in his discussion of cytoplasmic 

 constriction in these cells in his statement that : 



Die Tatsache, dass von jenen Zellen Plasmabestandteile wieder an de 

 Umgebung abgegeben werden, spricht dafiir, dass hier eine wirkliche 

 Umarbeitung stattgefunden hat. tjberhaupt ist die Abgabe von Sub- 

 stanzteilen durch l^anphocytare Zellen eine weit verbreitete Erscheinung; 

 sie lasst sich nicht nur bei gewohnlichen Lymphocyten im Bindegewebe 

 beobachten, sondern sie gebt, wie Dominici gezeigt hat, auch in gros- 

 sen Umfange bei bestimmten Tieren in Lyinpdriisen and Milz von sich 

 und sehr wahrscheinlich haben wir auch — -die neueren Untersuschungen 

 Wright's sprechen ziigunsten dieser Annahme — in den Blutplattchen 

 der Sanger Abschniirungen der Knochenmark — -Riesenzellen zu sehen, 

 die in die Zirkulation gelangen und dort der Auflosung anheimfallen. Da 

 die Riesenzellen selbst aus den l>Tnphoc}i:aren Formen des Knochen- 

 marks hervorgehen, waren diese Abschniirungen in Parallele zu setzen 

 zu jenen der Lymphocyten und Plasmazellen (p. 60). 



In view of the data just discussed concerning the origin of 

 plastids, may not similar considerations be extended to the cyto- 

 morphosis of the mammalian erythroblast? Recent morpholog- 

 ical investigators of the blood support the monophyletic view in- 

 volving the conclusion that erythroblasts, and this group of 

 plasma cells, megakaryocytes and lymphocytes are genetically 

 closely related, having a common origin either directly or indi- 

 rectly from mesenchymal cells. Consequently it would not appear 

 remarkable if it should be found that in both groups of cells similar 

 processes are involved in the contribution of morphological ele- 

 ments to the blood.'' That whereas in lower vertebrates the hemo- 



^ In connection with the subject of the formation of hemoglobin in the cyto- 

 plasm of the mesenchymal cell and its ultimate detachment from the nucleated 

 remainder it is not without interest to note that Shafer ('74) and also Ranvier ('74) 

 described the development of hemoglobin within the cj^toplasm of young connec- 

 tive cells from which it was later liberated into the circulation in the form of non- 

 nucleated corpuscles. Maximow ('09, p. 513) also records the observation in en- 

 dothelial cells of what appeared to be the constriction off of hemoglobin containing 

 portions of their cytoplasm. More recent investigators, while confirming the 

 observations, have not been able to accept the conclusion drawn from them by 



