22 CHARLES R. STOCKARD 



is seen to be well developed, the fins are already capable of 

 movement, and the brain and spinal cord are well shown and 

 covered with the black type of chromatophores. The heart is 

 seen to be more twisted than in the younger embryos and now 

 occupies a position further under the head of the specimen. The 

 network of vessels on the yolk-sac is beautifully mapped out by 

 the arrangement of the pigment cells, largely the red type of 

 chromatophore. It is to be especially noticed that pigment 

 cells are never present on the heart of the normal embryo. 



The other four figures of this group show individuals in which 

 there was no circulation of the blood, although the hearts pulsated 

 in a more or less feeble manner. In figure 5 the greatly distended 

 pericardium is again shown, the heart is stretched from the 

 head to the anterior surface of the yolk, and the lower part of 

 the heart is completely sheathed with pigment. All of the 

 pigment cells, however, are small and unexpanded. 



In figure 6, the heart is very greatly distended and filled with 

 plasma, yet it is apparently closed at one end since the plasma 

 is churned up and down and never pumped out of the heart. 

 In this case, there were several cells or particles suspended in 

 the plasma contained within the heart, and these particles 

 could be watched for long periods of time constantly moving 

 up and down but never going out of their confined position. The 

 pigment cells in this individual are greatly expanded, the red 

 type chromatophores showing beautiful mossy processes. The 

 lateral body cavities, Coe, or the coelomic spaces formed be- 

 tween the layers of the lateral plates of the mesoderm are greatly 

 distended with plasma. A condition particularly noticeable 

 in many such individuals. Red blood corpuscles are distinctly 

 seen throughout the entire extent of the intermediate cell mass 

 as indicated in the figure by the stippling in the posterior region 

 of the body and the tail. The heart of this specimen is also 

 richly covered with pigment and thus presents a striking con- 

 trast to the normal heart in figure 7. 



In figure 8 much the same condition is presented except that 

 here again the pigment cells are still contracted. The pericar- 

 dium, however, is distended and the heart is covered with pig- 



