190 THE PATH OF DEGENEEATIVE EVOLUTION 



grades of degradation according to the depth at 

 which it lives. This creature Cymonomus 

 which, when near the surface, has fully formed 

 eyes upon movable stalks, at a depth of a few 

 hundred yards exhibits movable stalks without 

 eyes; and at 1500 yards the stalks are fixed and 

 end in spines. 



Isopod Crustacea, which live in the deep sea, 

 present similarly degenerate eyes. Many are blind 



FIG. 65. Scolophlhalmus lucifugus, FAX. 



a, optic peduncle transformed to a spine. (After W. Faxon, The Stalk-eyed 

 Crustacea, Mem. of Mus. of Comp. Zool. Harvard College, vol. xviii., 1895.) 



and display all kinds of optic degeneration. Nocsa, 

 for instance, simply has eyes devoid of pigment. 

 Thus, in abysmal Crustacea, the degeneration of the 

 eyes is in no sense a retracing of developmental 

 stages. 



Another instance chosen from examples of the 

 atrophy of organs in individuals, shows that the 

 supposed law of retracing cannot be made uni- 

 versal. 



4. Atrophy of the branchial vessels in man. 

 Examination of a human embryo of about three 



