244 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



to the narrow slit mentioned above, which proceeds 

 from the lower circumference and penetrates to the 

 middle of the eye' (pp. 570, 571). 



"But the most striking discovery bearing on this 

 subject is that of the condition of the eyes in the em- 

 bryo and young compared with the adult of the blind 

 goby of San Diego. 



"In his essay on The Fishes of San Diego, Professor 

 Eigenmann briefly refers to and gives four figures 

 (Fig. 55) of the embryo of Typhlogobius, Mr. C. L. 

 Bragg having been fortunate enough to discover the 

 egg in the summer of 1891. 'The eyes develop nor- 

 mally, and those of No. 4 differ in no way from the 

 eyes of other fish embryos.' In this case, then, we 

 have the simplest and clearest possible proof of the 

 descent of this blind fish from individuals with eyes as 

 perfect as those of its congeners. 



" We have been permitted by the Director of the 

 United States National Museum to reproduce Profes- 

 sor Eigenmann's excellent figures on the embryo, 

 which tell the story of degeneration of the eye from 

 simple disease of the organ, the species being exposed 

 to conditions of life strikingly different from those of 

 its family living in the same bay. 



"Before the discovery of the eggs, the youngest in- 

 dividual ever seen is represented in Fig. 55, No. i, its 

 eyes being, though small, yet distinct, and ' appar- 

 ently functional.' 



" From these data it is obvious that future embryo- 

 logical study on cave-animals will farther demonstrate 

 their origin from ancestors with normal eyes." 



