PLATE 1 



EXPLANATION OF FIGURES 



1 to 12 u Erythrocytes at ditTerent stages of cytomorphosis. All drawings 

 except figures 1, 2 and 9 a are made from blood corpuscles within the blood vessels 

 in the foetal membranes surrounding the amniotic fluid of the pig embryo, care- 

 fully fixed in situ in the uteri, stained, cleared, and mounted in toto. All speci- 

 mens were stained with Giemsa's fluid. 



1 Young undifTereUtiated erythroblasts in the yolk sac of a 3 mm. emljryo, 

 showing large nuclei, spherical, basophilic cytoplasm, staincil, cleared and mount- 

 ed in toto. 



2 Erythrol)lasts in a large sinus of the liver, as seen in section; 7 mm. em- 

 bryo; ( p, partly differentiated erythroblast showing a more or less biconvex or 

 lens shape. 



3 ^iore highly differentiated erythroblasts, e, which have assumed biconvex 

 and cup forms; 2(3 mm. embryo. Non-nucleated erythrocytes or plastids pm are 

 beginning to appear in the circulation. 



4 Mature erythroblasts and jjlastids of various sizes; 30 nun. embryo. The 

 plastids now predominate numerically. 



5 and 6 Erythroblasts ec, which appear to be giving rise to plastids by a process 

 of cytoplasmic constriction, between the nuclear and cytoplasmic poles of the 

 cell (compare with figures 13 to 18) ; 26 mm. embryo. 



7 Erythroblasts with cytoplasmic process; 30 mm. embryo. 



8 Plastids with cytoplasmic process; 30 mm. embryo. By mechanical rotation 

 plastid a was demonstrated to be spherical in form. 



9 Erythroblasts in the telophase of mitosis, showing a thread of cytoplasm. 

 still connecting the daughter cells as suggestive of the mode of origin of cytoplas- 

 mic processes such as shown in figure 7; a, from vessel in foetal membrane of a 26 

 mm. embryo; 5, from section of heart of 7 mm. embryo. 



10 Group of corpuscles showing erythrocytic nuclei n with a narrow rim of 

 hemoglobin-containing cytoplasm; 30 mm. embryo. 



11 Group of corpuscles showing three erythrocytic nuclei, two of which /;/ cor- 

 respond to the so-called 'free nuclei,' evidently deficient in surrounding cytoplasm; 

 30 mm. embryo. 



12 Two erythrocytic nuclei ii, surrounded by a considerable rim of cyto- 

 plasm. Note flattened shape of nu(dei ; 30 mm. embryo. 



12 a Erythroblast containing two nuclei which have already assumetl a cup 

 shape; 30 mm. embryo. 



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