CONCLUSIONS ON THE EYE OF THE AMBLYOPSIS. 173 



material, completes it out of the material provided for the foundations, and that in 

 fact not even all of this (lens) material enters into the structure of the adult eye. 

 The development of the foundations of the eye are phylogenetic, the stages beyond 

 the foundations are direct to the present adult condition of the eyes from which 

 they are now ontogenetically degenerating to the vanishing point. 



CONCLUSIONS. 



The study of the development and its related questions shows: 

 i. The eye of Amblyopsis appears at the same stage of growth as in fishes 

 developing normal eyes. 



2. The eye grows but little after its appearance. 



3. All the developmental processes are retarded and some give out prematurely. 

 The most important of the latter is the cell division and the accompanying growth 

 that provides the material for the eye. 



4. The lens appears at the normal time and in the normal way, but its cells 

 never divide and never lose their embryonic character. 



5. The lens is the first part of the eye to show degenerative steps and it disappears 

 entirely before the fish has reached a length of 1 mm. 



6. The optic nerve appears shortly before the fish reaches 5 mm. in length. It 

 does not increase in size with the growth of the fish and possibly never develops 

 normal nerve fibers. 



7. The nerve does not increase in size with growth of the fish. 



8. The optic nerve gradually loses its compact form, becomes flocculent, 

 dwindles, and can not be followed by the time the fish has reached 50 mm. in 

 length. In the eye it retains its compact form for a much longer time, but disap- 

 pears here also in old age. 



9. The scleral cartilages appear when the fish is 10 mm. long; they grow very 

 slowly — - possibly till old age. They do not degenerate at the same rate as other 

 parts of the eye, if they degenerate at all. 



10. The history of the eye may be divided into four periods: 



(a) The first period extends from the appearance of the eye till the embryo 

 reaches 4.5 mm. in length. This period is characterized by a normal 

 palingenetic development except that cell division is retarded and there 

 is very little growth. 



(b) The second period extends from the first till the fish is 10 mm. long. 



It is characterized by the direct development of the eye from the nor- 

 mal embryonic stage reached in the first period to the highest stage 

 reached by the Amblyopsis eye. 



(c) The third period extends from the second period to the beginning of 



senescent degeneration, from a length of 10 mm. to about 80 or 100 

 mm. It is characterized by a number of changes which, while not 

 improving the eye as an organ of vision, are positive as contrasted 

 with degenerative. There are also distinct degenerative processes 

 taking place during this period. 



(d) The fourth period begins with the beginning of senescent degeneration 

 and ends with death. It is characterized by degenerative processes only 

 which tend to gradually disintegrate and eliminate the eye entirely. 



