94 FEANKLIN P. REAGAN 



either active or passive. Such changes would take place in em- 

 bryos whose hearts were solid. The region mesial to the optic 

 cups, and sometimes the snout, displayed such patches of eryth- 

 rocytes. Blood sometimes developed in the dilated portions of 

 hearts which were solid at both ends. In some cases the heart 

 had solid extremities, but contained a number of blood-bearing 

 dilations. 



Figures 49 to 60 are sketches of the dorsal cephalic surface of 

 living embryos whose blood-circulation was prevented by chemi- 

 cal means. In some of these embryos the heart was solid at one 

 extremity or both, or solid throughout. The stippled areas rep- 

 resent these patches of erythrocytes. Whenever such an area 

 was sectioned and stained, the same group of cells could be lo- 

 cated in section, the erythrocytes staining intensely red in my 

 modification of Mann's methyl blue-eosin stain. The surround- 

 ing mesenchyme would stain a light or intense blue. In some 

 cases the hematopoetic areas found in section were larger than 

 one should expect from the sketches of the living condition. This 

 probably means that cells may stain intensely red even though 

 they are not visible in the living condition. In no case was the 

 eosinophilous region smaller than the group of erythrocytes 

 seen in the living conditions. The method of chemical treat- 

 ment is either given in the text with the discussion of each embryo 

 or with the explanation of the figures. Figures 49 to 56 show dor- 

 sal views of the cephalic regions; figures 57 and 58 are lateral 

 views. The nature of the heart and the distension of the peri- 

 cardium can be observed in these figures. 



In the embryo from which figure 49 was taken, several blood 

 lacunae could be seen on the dorsal surface. Two such layers 

 are located dorso-mesial and two are dorso-posterior to the eyes; 

 a fifth median group is found dorsally located in about the 

 transverse plane of the posterior limits of the eyes. Each of 

 these groups of cells, together with certain others which were in- 

 visible in the living condition, were found when the embryo was 

 sectioned. They are illustrated in figures 67 to 70. The heart 

 of this embryo was, from the first, solid at both ends. 



