5O LIBBIE H. HYMAN. 



PLATE II. 



FIGS. 22 TO 26. Disintegration of a heart of eleven to twelve somites showing 

 increased susceptibility of the middle of the right side. 



FIGS. 27 TO 31. Heart of a sixteen somite chick, showing restoration of simple 

 direct gradient from the sinus to the arterial end. Disintegration in the sinus 

 begins at the exact places of initiation of the heart beat, indicated in Fig. 27 by 

 arrows. 



FIGS. 32 TO 35. Heart of twenty somites, similar to the preceding. 



FIGS. 36 TO 39. Heart of thirty somites, showing heightened susceptibility of 

 the ventricular bend and the auricular evaginations, indicating rapid development 

 of these regions at this time. 



FIG. 40. Ventral view of an abnormal heart of a chick embryo of thirteen 

 somites, obtained by incubation at subnormal temperature, showing inhibition of 

 the bend to the right, and abnormally enlarged arterial end. The nervous system 

 is normal but the posterior end of this chick (not shown in the drawing) is inhibited 

 as discussed in the preceding paper. 



FIG. 41. Ventral view of another abnormal chick of the same lot as Fig. 40 

 showing reduced sinus region as compared with arterial region. This chick also 

 has an inhibited posterior end, not shown. 



