250 CHARLES R. STOCKARD 



appearance when compared with a normal individual, such as 

 the one of eight days shown in figure 7. 



Figures 10 and 11 illustrates two specimens of Fundulus 

 majalis drawn to the same scale as the previous figures. The 

 egg of this species is considerably larger than that of heterocli- 

 tus, but its response to the experimental treatment is the same. 



Figure 11 represents a normal embryo eight days old. It is 

 seen not to be comparatively so far advanced at this period as 

 is the heteroclitus, since its development is much slower and it 

 requires from five to ten days longer to hatch. Very little pig- 

 ment is present, yet the vessel net is well formed on the yolk- 

 sac and the heart is distinctly seen to be more or less S-shaped. 



Figure 10 is an embryo of the same age that had been subjected 

 for forty-eight hours to a solution of 2 cc. of 95 per cent alcohol 

 in 50 cc. of sea-water. Scarcely any pigment is present, the 

 pericardium is typically distended and the heart is stretched 

 into a long conical shape. No vessels are seen upon the yolk. 

 The posterior end of the embryo is not shown in the figure, but 

 in it could be seen early blood cells in the intermediate cell mass 

 while a few small blood islands were present on the yolk-sac 

 near the posterior end of the embryo. 



After these eight- or ten-day stages very few changes of interest 

 take place. The normal embryos hatch at from eleven to four- 

 teen daj's as a rule, and become free swimming. The individuals 

 without a circulation of the blood never succeed in breaking out 

 of the egg membrane but may remain alive for twenty-five or 

 thirty daj^s in some cases, and almost all of them will live at 

 least sixteen to twenty days. The red blood corpuscles are 

 very distinctly noticeable in these older individuals and can be 

 seen to remain permanently in their original places of origin. 

 The intermediate cell mass may cease to be distinguishable, 

 as was evident in the old specimens. This, however, is not due 



Figs. 15 to 20 Living embrj-os sixteen days old, without blood circulation, 

 showing variations in the pericardial distension, the position of the heads, and 

 the perculiar heart conditions. These hearts, ht, all pulsate feebly and in several 

 figures the slight lifting of the anterior yolk membrane is shown; this small mem- 

 branous cone is rythmically raised with the pulsations. 



