DROSOPHILA BRED IN THE DARK. 3OI 



medium which are changed at intervals as shown by Woodruff's 

 experiment (Archiv fur Protistenkunde, 'u). 



In caves conditions are practically uniform. Also in dark 

 corners under stones and logs, conditions are more'nearly uni- 

 form than in the open. Since it seems almost certain that forms 

 which now inhabit caves once- lived outside under stones and in 

 dark corners and that they had varied in the direction of cave 

 animals before they entered cavi -, is it not possible that the 

 more nearly constant environment of the dark corners under 

 stone- and lo-s ha- st.irted the degenerative change-; which have 

 been carried to their present condition in the more constant 

 en\ ironiiu-ni of tin- ra\ Po be -lire .ill changes in rave animals 



not degenerative. The tactile sense, for example, becomes 



highly developed, but no doubt a sec >nd (\ui-viti\e fart..r eir 

 here. 



