ERYTHROBLASTS IN THE PIG EMBRYO 137 



In man for example, Weber ('46) who seems to have been the 

 first to give a description of the nucleated red cells of a 12-weeks 

 human embryo, concluded that these cells are spherical in form and 

 describes them as "glatte kernhaltige Kiigelchen von 0.0042" mit- 

 tlerer Grosse." Also Engel in 1899, referring to human embryos 

 of about 40 mm. draws a similar conclusion and states that ''Die 

 Metrocytes I und II Generation sind kugelige, selten ellipsoide 

 Zellen, mit einen runden Kern, der bei den Metrocytes I Genera- 

 tion ein Drittel bis die Half te, bei denen II Generation ein SechsteJ 

 bis ein Achtel des Protoplasmaleibes betragt" (p. 34), These 

 statements are apparently accepted in even the recent literature on 

 the human embryo as presenting an essentially correct account of 

 the form of the erythroblast. On the other hand, it is important 

 to note that soon after Weber's paper, Kolhker ('46) gave quite 

 a different description of the erythroblast s of a 3-months human 

 embryo. He stated on the contrary that ''Die meisten Korper- 

 schen sind platt, wenige vertieft oder vollkommen kugelig, eine 

 noch geringere Zahl derselben, und zwar im Leberblute, rundlich 

 elliptisch" (p. 113), and concludes that "Die farbigen kernhaltigen 

 Blutkorperchen platten sich je alter sie werden immer mehr ab, 

 bekommen selbst leicht Excavationen" (p. 157). In the 2.5 cm. 

 cat embryo, Howell ('91) describes finding red corpuscles which 

 were "large, oval and nucleated, resembling somewhat the cor- 

 puscles of the reptile or amphibia. In shape they were biconcave, 

 irregular, or apparently, in some cases, biconvex" (p. 59). It may 

 be further noted that even in the lower vertebrates, where of 

 course the erythrocytes are with few exceptions alway nucleated, 

 there is evidence according to Gage ('88) for Petromyzon marinus, 

 and Dekhuyzen ('99, '01), for Petromyzon fluviatilis, that nucle- 

 ated red cells may become biconcave and concavo-convex or bell 

 shape (in the latter case designated 'chromokrateren' by Dekhuy- 

 zen) ; nor should it be overlooked that Dekhuyzen ('99) describes 

 the occurrence of nucleated cup-shaped forms in the bone mar- 

 row of the rat, guinea-pig and rabbit, and draws the conclusion 

 that "Bei der Autogenese der roten Blutkorperchen der Siiugetiere 

 tritt die ancestrale becherformige rote Blutzelle als ein bald vor- 

 iibergehendes Stadium auf" (p. 211). 



