101 



Parker, '!)().— The eyes in blind crayfisli. 



Bull. Mus. Comp. Zool., xx, pp. 153-162, plate i. 

 Parlver, '91.— The Compound eyes in crustaceans. 



Bull. Mus. Comp. Zool., xxi, pp. 45-140, plates i-x. 



The History of the Eye of Amblyopsis. 



C. H. ElGENMANN. 



[Abstract.] 



A. DEVELOPMENT. 



The eye of Amblyopsis appears at the .same stage of growtli tliat it 

 appears in fishes developing noi'mal eyes. 



The eye grows but little after its appearance. 



All the developmental processes are retarded and some of them give 

 out prematurely. The most important of the latter is the cell division 

 and the accompanying growth that provides tlie material for the eye. 



The lens appears at the normal time and in the normal way. l)ut its 

 cells never divide and never lose their emliryonic character. 



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. 



The optic nerve appears shortly before the fish reaches ."> mm. in 

 length. It does not increase in size with the growth of the fish and pos- 

 sibly never develops normal nerve fibers. 



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



The optic nerve gradually loses its compact form, becomes fiocculent, 

 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 disappears here also in old age. 



The scleral cartilages appear Avhen the fish is 10 mm. long; they grow 

 very slowly— possibly till old age. They do not degenerate at the same 

 rate as othm- parts of the eye if they degenerate at all. 



