34 CHARLES R. STOCKARD 



Figure 25 is a section through another heart of the same age. 

 In this a huge pigment cell is shown within the heart cavit}'. 

 It is recalled that pigment cells were frequently seen to lie 

 along these abnormal hearts while chromatophores were never 

 present on the normal heart. The endothelium in figure 25 

 is more or less broken and the general condition of the heart is 

 poorly developed. 



In figure 26, a section is illustrated through a heart as it leads 

 into the aortic arches. Here also large pigment cells are present. 

 The endothelium is indicated in several places and within the 

 cavity of this heart is a mass of periblastic material. It would 

 look as though the periblast had been sucked from the surface 

 of the yolk into the heart ca\'ity. Several large periblast nuclei, 

 pb, are indicated and are easily recognized on account of their 

 amorphous shape and huge size. 



In figures 26 and 28 there are several cells, c, of a question- 

 ably degenerate type, the cytoplasm of which stains an extremely 

 red color while the nucleus is small and pycnotic in appearance. 

 These cells might in cases be looked upon as some type of wan- 

 dering cell, but in most instances they are very degenerate in 

 appearance. 



It must be distinctly noticed that in none of the figures are 

 erythroblasts shown. Throughout these heart regions at all 

 stages the observer is impressed by the entire absence of any 

 form of red blood cells in embryos that have absolutely had 

 no circulation. One must constantly guard against the possi- 

 bility of a slight circulation having existed for a short time and 

 then having ceased. Another reason for blood movement may 

 be the twisting or twitching reactions of the embryonic body. 

 Conclusions regarding the permanent position of blood must 



Figs. 29 and 30 Two sections through different parts of the heart in an em- 

 bryo sixteen days old, without a blood circulation; Embryo 314. 



Fig. 29 The aortic end of the heart, an almost solid mass with endocardial, 

 EC, cells near the center. 



Fig. .30 Through the string-like portion of the same heart: ph, periblastic 

 nuclei and material completely fill the heart cavity; EC, endocardial cells; Ch, 

 chromatophores surrounding the heart wall. The upper part of the section is 

 cut slightly oblique. 



