101 



Parker, '90.— The eyes in blind crayfish. 



Bull. Mus. Comp. Zool., xx, pp. 153-102, plate i. 

 Parker. '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 Aml)lyopsis appears at the same stage of growth that 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 tlie cell division 

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



The lens appears at the normal time and in the normal way. Imt its 

 cells never divide and never lose their endjryonic 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 5 mm. in 

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

 sil)ly never develops normal nerve fillers. 



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



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

 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 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. 



