194 BULLETIN OF THE BUREAU OF FISHERIES. 



stimulating effects on the lateral-line organs. In this respect my results agreed with 

 those of Bugnion (1873, p. 302), who experimented with salt solutions upon the 

 lateral-line organs of Prott us. 



Food. — The normal stimulus for taste in animals, as in the human being, is the 

 dissolved material in their food. Judging from the aquarium habits of some fishes, 

 they seek their food chiefly by the eye, but it is also possible that the juices of the 

 food may excite them. To ascertain whether the lateral-line organs are thus stimu- 

 lated, I placed a single individual of JFundulus heterocHtus in a small vessel of sea 

 water and. alter it had become quiet, endeavored to discharge from a capillary tube 

 some mussel juice on the lateral line of the body, the substance of Mytilms edulis 

 being a favorite food of this fish. The extreme activity of the fish made such an 

 experiment rather difficult, but after frequent trials on several individuals I got no 

 results that could be said to indicate that the lateral-line organs were stimulated. 



In a second set of experiments I etherized the fishes and cut the spinal cord just 

 behind the head. After recovery, such fishes act as though the trunk muscles were 

 paralyzed and swim about slowly by the pectoral tins. If properly fed they live for 

 a week or more. They often rested on the bottom of the vessel in which they were 

 kept, and when quiet afforded an excellent opportunity for testing the lateral-line 

 organs. But even under these circumstances I never obtained reactions from these 

 fishes that led me to conclude that the sea water decoction of mussel discharged on 

 their lateral lines ever stimulated these organs. In this respect my results agreed 

 with those of Bateson (1890, p. 237). and I conclude that the lateral-line organs are 

 not stimulated by food. 



Oxygen. — The oxygen dissolved in sea water is essential for the life of marine 

 fishes, and as the amount varies in different parts of the sea. it is possible that this 

 substance may serve as a stimulus to the lateral-line organs. To test this possibility, 

 specimens of Fundulus heterocUttts, normal and cut, were introduced into sea water 

 that had been boiled to expel the dissolved gases and then cooled with as little 

 exposure to air as possible. When the fish were introduced they swam rapidly 

 throughout the whole vessel, and their respiration was characterized by rapid and 

 deep swallowing movements. These features disappeared very quickly on transfer- 

 ring the fish to ordinary sea water. Since normal and cut fishes acted alike in this 

 experiment, there was no reason to suppose that lack of oxygen was in any way a 

 stimulus for the lateral-line organs. 



Carbon dioxide. — As carbon dioxide is one of the most extensive waste products 

 from animals* bodies, it might be regarded as a possible means of polluting water, and 

 the lateral-line organ-, might serve to detect this pollution. To ascertain whether 

 carbon dioxide was a stimulus for these organs, normal and cut individuals of 

 l-'mnhihis heteroclitus were introduced into sea water through which carbon dioxide 

 gas had been bubbling in minute streams for over half an hour. Both classes of 

 fishes acted as though they were in ordinary sea water, and there was no reason to 

 conclude that carbon dioxide had any effect upon the lateral-line organs. 



Foidness of water. A quantity of foul water taken from a vessel in which 

 marine animals and plants were decaying was mixed with sea water and cut and 

 normal individual- were introduced into it and their reactions observed. Although 

 this mixture had a most offensive odor to the experimenter, the two sets of fishes 



