PREFACE. IX 



Mr. Lewis H. Wild, under the direction of Prof. J. Reighard, made a series of 

 photographs of entire eggs and embryos (plate 7). 



Mr. Samuel Garman sent me my first specimens of the blind fish, Troglichthys. 



Dr. B. W. Evermann of the Bureau of Fisheries and the late Prof. W. Norman 

 secured me specimens of Typhlomolge. 



Prof. Wm. Roux, Dr. F. R. Lillie, and others kindly consented to the repub- 

 lication of articles issued in the journals under their editorship. 



I desire also to express my high appreciation of the interest taken by the authori- 

 ties of Indiana University, especially by President William Lowe Bryan, in the 

 various trips and plans necessary to bring this work to a successful conclusion. 



The present work forms No. 97 of the Contributions from the Zoological Lab- 

 oratory of the Indiana University. 



Finally, I wish to express my indebtedness to her who as Rosa Smith guided 

 me to the blind-fish rocks at the base of Point Loma, and who as Mrs. R. S. Eigen- 

 mann collected for me at the same place, has acted as editor of the various papers 

 that have appeared, and through the twelve years during which my leisure has 

 largely gone to the blind vertebrates has ever been ready with advice, encour- 

 agement, and assistance. 



CONCLUSIONS OF GENERAL] IMPORT. 



(1) The bleached condition of animals living in the dark, an individual envi- 

 ronmental adaptation, is transmissible and finally becomes hereditarily fixed. 

 (See page 80.) 



(2) Ornamental secondary sexual characters not being found in blind fishes 

 are, when present, probably due to visual selection. (See page 94.) 



(3) Individual degeneration of the eye may begin in even earlier stages of 

 development until nearly the entire development becomes affected, that is, func- 

 tional adaptations are transmissible. (See pages 172 and 235.) 



