ERYTHROB LASTS IN THE PIG EMBRYO 149 



and in still later stages almost entirely, of non-nucleated hemo- 

 globin elements or erythrocytes. 



Confining om- attention to these non-nucleated elements or 

 plastids, as they occur in embryos between 10 and 35 mm., it 

 will be observed that they vary greatly in size, ranging from the 

 average sized plastids (fig. 29, 30 and 4 pm) to the large so-called 

 macrocytes on the one hand (figs. 4 pi and 31), to microcytes, on 

 the other hand, some of which are even comparable to blood 

 platelets in size (figs. 4 ps, 11 ps, 26 and 27). The presence of the 

 latter smaller plastids is in interesting contrast to adult mam- 

 malian blood where, as is frequently stated, that hemoglobin con- 

 taining bodies the size of blood platelets do not occur in normal 

 blood. But that -even these smaller plastids in the early pig 

 embryo in the majority of cases are hemoglobin containing ele- 

 ments is unquestionably indicated by their yellowish color in 

 fresh preparations and their characteristic hemoglobin stain 

 with Giemsa (figs. 4 and 11, ps). Engel gives no account of these 

 smaller hemoglobin corpuscles, but their frequent and constant oc- 

 currence in both fixed and fresh blood, .in the latter case, examined 

 while still within the living vessels, seems to leave no doubt but 

 that they are to be regarded as normal elements in the blood of 

 the pig embrj^o at this stage of development. 



In form these non-nucleated corpuscles vary from rounded or 

 spherical structures (figs. 27 and 28) to biconcave discs (fig. 31) 

 and concavo-convex or cup-shaped elements (figs. 29, 30 and 4). 

 The spherical form appears to be more characteristic of the smaller 

 plastids, although even some of these can be demonstrated to 

 have a disc shape (fig. 26). ^^^lile some of the medium sized 

 and larger plastids may be spherical (fig. 28), the majority are 

 either biconcave discs or bell shaped the latter form being ap- 

 parently predominant (fig. 4). Engel ('99) recognizes a varia- 

 tion in size of these non-nucleated erythrocytes, but describes 

 them all as spherical in shape, stating that in the 35 mm. pig 

 embryos "Dellen sind meistens nicht nachweissen" (p. 41), and 

 that in the 40 nmi. pig ' ' Trotz der grossten Sorgfalt, welche ich 

 auf die Anfertigimg der Praparate verwenden konnte, war es 

 meistens nicht moglich Praparate mit kreisrunden dellenhaltigen 

 Blutscheiben zu erlangen" (p. 45), a conclusion which it seems 



