THE BLINDNESS OF THE CAVE I- A I NA. 



57 



directly. The writer noticed not infrequently that the eyes of 

 the cross between Fundiiliis and Menidia were normal in the 

 beginning but appeared more abnormal the further the develop- 

 ment progressed. We will illustrate this statement by two series 

 of drawings. The first case is illustrated by Figs. 3 to 6. Fig. 3 

 shows the embryo four days old. The embryo has normally 

 developed eyes w r ith lenses. The embryo's heart, which is 

 visible in front, was not yet beating and no pigment w r as formed. 

 The same embryo is shown two days later in Fig. 4. The eyes 

 instead of developing any further are less distinct. Fig. 5 is the 

 same embryo two days later (eight days old). The eyes are 



/BEATING HEART 



FIG. 6. 



hardly recognizable, it is difficult to decide without sectioning 

 whether the lens still exists. The internal ear is distinguish- 

 able. The heart is pulsating. 



Fig. 6 shows the same embryo at the age of two \veeks. 

 Apparently the pigment is the only organ of the eye which is 

 developed. 



