THE BLINDNESS OF THE CAVE FAUNA. 65 



V. 



The writer was anxious to know whether it was possible to 

 produce deficiencies in the eyes of Fundulus by raising them in 

 the dark. It was necessary to carry on such an experiment with 

 a large number of embryos. Since it was possible that a short 

 exposure of the unfertilized egg or of the sperm to the light might 

 already have some effect, the females and males of Fundulus 

 heteroclitus to be used for the experiment were put into an abso- 

 lutely dark room where everything was prepared for the experi- 

 ment. The females and males were stripped of their sexual cells 

 in the dark and the jars containing both sperm and eggs were 

 put into dark boxes and kept in the dark room for four weeks. 

 Although many embryos had died, hundreds had survived. All 

 had perfectly normal eyes. This experiment confirms similar 

 experiments made by the writer in previous years. 



All these experiments show that while it is comparatively easy 

 to produce blind Fundulus embryos, or, more correctly speaking, 

 fish with degenerated eyes, by heterogeneous hybridization or by 

 low temperature or by lack of oxygen (or by an excess of mag- 

 nesium salts or by alcohol, as shown by Stockard and McClendon) 

 no such result can be produced by lack of light. 



VI. 



If we consider all the facts in the case there is nothing at 

 present to warrant the assumption that the blind cave animals 

 owe the deficient development of their eyes to the lack of light, 

 since lack of light is according to our present knowledge a less 

 efficient agency in the causation of an abnormal development 

 of the eye than a number of other injurious influences. Under 

 these conditions we must be prepared to consider the possibility 

 that many if not all the blind species found in caves owe their 

 blindness to other influences than those of the cave. Eigenmann 

 states that no blood vessels enter the eye of the blind cave 

 salamander Typhlotriton. Since the experiments of Uhlenhuth 

 as well as those of Stockard and of the writer reported in this 

 paper indicate the importance of the circulation and of chemical 

 factors in the development of the eyes it is not impossible that 

 in the blind fish (Amblyopsidae) as well as in the blind sala- 



