^INTRODUCTION. 



In the present paper I propose to describe the developmental stages of the eye 

 of the blind fish Amblyopsis spelseus and the modifications the eye undergoes during 

 growth, maturity, and old age. Questions of special interest in the history of this 

 very degenerate organ are : 



1. Do the rudiments of the eye make their appearance as early as usual or later? 



2. How much does the eye grow from the time of its appearance? 



3. When does each part of the eye reach its maximum (a) in size, (b) in mor- 

 phogenic development, (c) in histogenic development? 



4. When does the eye as a whole reach its maximum development? 



5. Are there evidences of a slowing down of the rate of the developmental 

 processes : (a) cell division, (b) cell arrangement, (c) cell differentiation? 



6. Are there evidences of a cutting off of late developmental stages, that is, are 

 there any parts of the normal eye that are not developed? 



7. Does the eye develop directly toward the condition of the adult or does it 

 follow palingenic paths and then retrograde to the condition found in the adult? 



8. What parts of the eye degenerate first? 



9. What is the comparative rate of the ontogenetic degenerative modifications 

 of the various parts of the eye, and how does their rate compare with the rate of phy- 

 logenetic degeneration implied by the structure of the adult eye of Amblyopsis and 

 the different stages of degeneration reached by other members of the family? 



10. Is there any evidence for or against the dictum of Sedgwick that structures 

 which have disappeared from the adult organization are retained in the embryo only 

 if the organ was of use to the larva after it had ceased to be of use to the adult? 



The material on which this paper is based was collected at various times since 

 1896, in part by a grant from the trustees of the Elizabeth Thompson Science Fund, 

 and in part by a grant from the American Association for the Advancement of Science. 

 All of it came from caves near Mitchell, Indiana, on the Monon Railroad, to whose 

 officials I wish to express my indebtedness for many favors* By legislative act these 



* We have found that the specimens of Cambarus pellucidus coming from these caves have an eye structure 

 much more degenerate than specimens of the same species from Mammoth Cave. I have not been able to secure 

 Amblyopsis from Marrmcth Cave to see whether there is a similar difference in the eyes of the fishes from the 

 two localities. 



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