242 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



Stages, and appear to lack but the pigment.' In the 

 bhnd cave-shrimp (Troglocaris) of Austria, Dr. Joseph 

 discovered that the embryo in the egg is provided with 

 eyes. 



" In this connection should be recalled the observa- 

 tions of Semper in his Animal Life (pp. 80, 81) on Pin- 

 notheres holothuricB, which lives in the * water-lungs ' 

 of holothurians, where, of course, there is an absence 

 of light. The zoea of this form has large 'well-de- 

 veloped eyes of the typical character. Even when 

 they enter the animal they still preserve these eyes ; 

 but as they grow they gradually become blind or half- 

 blind, the brow grows forward over the eyes, and 

 finally covers them so completely that, in the oldest 

 individuals, not the slightest trace of them, or of the 

 pigment, is to be seen through the thick skin, while, 

 at the same time, the eyes seem to undergo a more or 

 less extensive retrogressive metamorphosis.' 



"In this connection may be mentioned the case of 

 the burrowing blind shrimp {Caliianassa stinipsonii^, 

 which has been found by Prof. H. C. Bumpus, at 

 Wood's Holl, Mass., living in holes at a depth of be- 

 tween one and two feet. He has kindly given me a 

 specimen of the shrimp, which is blind, with reduced 

 eyes, smaller in proportion to the body than those of 

 the blind crayfish. He has also obtained the eggs, 

 and has found that the embryos are provided with dis- 

 tinct black, pigmented eyes, which can be seen through 

 the egg-shell. 



"Recently, Zeller has studied the embryology of the 

 Proteus of Adelsberg Cave, and has confirmed the 

 statement of Michahelles, who, in 1831, discovered 

 that the eyes of this animal are more distinct in the 



