180 



THE AMERICAN NATURALIST [Vol. XLIV 



are still in use, except when living in caves; in the latter they have not 

 been in a position to be used for hundreds of generations. The transi- 

 tion between conditions of possible use and absolute disuse may have 

 been rapid with each individual after permanently entering a cave. 

 Panmixia, as regards the minute eye, continued. Reversed selection 

 was inoperative, for economy can not have affected the eye for reasons 

 already stated. Simply the loss of the force of heredity, unless this 

 was caused by disuse or the process of germinal selection, can not have 

 brought about the conditions, because some parts have been affected 

 more than others. 



Considering the parts most affected and the parts least affected, the 

 degree of use is the only cause capable of explaining the conditions. 

 Those parts most active during use are the ones reduced most, viz., 

 the muscles, the retina, optic nerve and dioptric appliances, the lens 

 and vitreous parts. Those organs occupying a more passive position, 

 the scleral cartilages, have been much less affected and the bony orbit 

 least. The lens is one of the latest organs affected, and not at all 



It disappears most rapidly after the beginning of absolute disuse 

 both ontogenetically and phylo^enetically. All indications point to use 

 and disuse as the effective agent in molding the eye. The process does 

 not, however, give results with mathematical precision. In Typh- 

 lichthya Bubterraneua the pigmented layer is affected differently from 



different species' would offer another objection if we did not know of 

 the variable condition of these structures in different individuals. 

 Chilton has objected to the application of the Lamarckian factor to 

 explain degeneration on account of the variable effects of degeneration 



In the Biological Bulletin for January, 1905, Professor Eigen- 



from Horse Cave. Kentucky, and Typhlichthys icyandotte, from 

 Cory don, Indiana, near the large Wyandotte Cave. 



In the Field Columbian Museum, February, 1909, Dr. Seth 

 E. Meek describes a number of species from Tropical America. 

 These are: Rhamdia nasula, from Buenos Aires de Terraba, 

 Costa Rica; Aslyanax rcgani. from Las Cafias, Costa Rica; 

 Cyprinodon dearborn*, from Willemstad, Curacao, Dutch West 

 Indies; Girardinus vandepolli, from Curacao; Per c ilia caudata, 

 from Turrubares, Costa Rica; Cichlasoma punctatinn, from 

 Buenos Aires de Terraba. Costa Rica: and Cichlasoma frontale, 

 from Turrubares, Costa Rica. 



In the Proceedings of the Zoological Society of London, 1909, 



