56 JACQUES LOEB. 



fish found in caves w T hich also have some of the elements of an 

 eye but in a condition unfit for use. The term "blind fish" is 

 therefore used in the following as synonym with imperfect or 



degenerated eyes. 



III. 



BLINDNESS PRODUCED THROUGH HETEROGENEOUS CROSSINGS. 

 Figs, i and 2 are camera drawings of hybrids between Fundulus 

 heteroclitus 9 and Menidia d" . The first embryo is eight, the 

 second fourteen days old. In neither of these two embryos are 

 eyes noticeable, though of course a histological examination 

 might have divulged rudimentary eyes. The embryos are in this 



BEATING 

 HEART 



FIG. 5. 



respect to all appearances comparable to the blind cave fish or 

 salamanders. 



It is a known fact that certain blind animals have in an early 

 stage a comparatively better developed eye than in later stages, 

 i. e., that the eye either stops developing early while the develop- 

 ment of the rest of the body continues or that the eyes degenerate 



