OLFACTORY REACTIONS OF FUNDULUS 5 



In order to carry out tests against which the objection could 

 not be raised that the results might be due to the shock of cutting 

 nerves rather than to the loss of a sense organ, the following pro- 

 cedure was employed. By taking two stitches of very fine silk- 

 thread one on either side of the anterior olfactory aperture, it was 

 comparatively easy to close this aperture and thus to prevent any 

 passage of water through the olfactory sacs. Killifish, which pre- 

 vious to the operation gave markedly different and characteristics 

 reactions to the two classes of cloth packets already described, 

 reacted to both kinds of packets after their anterior olfactorj^ 

 apertures were closed, as they had previously done to the packets 

 that contained no food. That this reaction was not to be directly 

 attributed to the operation of stitching up the apertures, was dem- 

 onstrated in two ways. If, after the stitches were taken, the thread 

 was not drawn up and tied so as to close the aperture, but the 

 ends were allowed to remain free, the fish would react as normal 

 fish do to the two classes of cloth packets, thus showing that the 

 mechanical injury due to the stitches themselves did not influence 

 the fish in any essential way. Further, if fishes whose anterior 

 olfactory apertures had been closed by stitching and tying and 

 whose discrimination for the two classes of packets had thereby 

 been lost, had their olfactory apertures reopened by cutting and 

 removing the thread, they very soon regained their capacity to 

 distinguish packets with food from those without food; in other 

 words, they soon returned to the condition of normal fishes. For 

 these reasons, I believe that stitching up the anterior olfactory 

 aperature is in itself not a disturbing operation for the fish and 

 that the loss of the ability to recognize the presence of hidden food 

 under these circumstances, is in reality due to the loss of the ol- 

 factory function. I, therefore, conclude that Fundulus heterocli- 

 tus, like the catfish, uses its olfactory apparatus as an organ with 

 which to scent its food; i. e., its olfactory apparatus is a chemical 

 distance-receptor of very considerable importance in its daily * 

 activities. 



