Adaptation to Environment 325 



isms; and conversely, animals which are not provided 

 with visual mechanisms can hold their own in the open, 

 where they meet the competition of animals which 

 can see, only under exceptional conditions. This seems 

 to account for the fact that in caves blind species are 

 comparatively more prevalent than in the open. 



In other words, the adaptation of blind animals to 

 the cave is only apparent; they were adapted to cave 

 life before they entered the cave. Many animals are 

 obviously burdened with a germinal abnormality 

 giving rise to imperfection and smallness of the eye — 

 the hereditary factor involved may have to do with 

 the development of the blood-vessels and lymphatics 

 of the eye. Such mutants can survive more easily in 

 the cave, where they do not have to meet the competi- 

 tion of seeing forms, than in the open. In man also an 

 hereditary form of blindness is known, the so-called 

 hereditary glaucoma. It has nothing to do with light, 

 but the disease seems to be due to an hereditary 

 anomaly of the circulation in the eye. 



Kammerer 1 has recently reported that by keeping 

 the blind European cave salamander Proteus anguinus 

 under certain conditions of illumination he succeeded 

 in producing two specimens with larger eyes. Accord- 

 ing to him the eyes of Proteus may develop to a 

 certain point and then retrogress again. He states 

 that by keeping young salamanders alternately for a 

 1 Kammerer, P., Arch. f. Entwcklngsmech., 1912, xxxiii., 349. 



