THE BLINDNESS OF THE CAVE FAUNA. 



55 



pean eyes by altering the constitution of the sea water (addition 

 of magnesium salts or of alcohols and other narcotics.) 1 The 

 writer's attention to an abnormal development of the eyes in 

 this embryo was first attracted in his experiments on hetero- 

 geneous hybridization. 2 He noticed that among the anomalies 

 noticeable in heterogeneous fish hybrids the lack of circulation 

 was the most common, but that incomplete or abnormal develop- 

 ment of the eyes was not infrequent. Such embryos often give 

 the impression that they have no eyes at all, though in reality a 

 histological analysis would probably show that some of the 

 organs of the eye are present. But it is safe to say that the 



BEATING HEWVT 



FIG. 4. 



condition of the eyes is such as to make them unfit to form a 

 retina image and for this reason we may call these embryos with 

 abnormal (or apparently lacking) eyes blind; in the same sense 

 in which this term is used in the case of the blind salamanders or 



1 Stockard, Am. Jour, of Anatomy, 10, 369, 1910; Jour. Ex p. Zoo/., 4, 165, 1907; 

 6, 286, 1909; McClendon, Am. Journ. Physiol., 29, 289, 1912. 



- Loeb, "Heredity in Heterogeneous Hybrids," Jour. Alorphol., XXIII., p. i, 

 1912. 



