FUNCTION OF LATERAL-LINE ORGANS IN FISHES. H>3 



Since in all these temperature experiments the normal fish and the cut ones 

 reacted in essentially the same way. I conclude that heat is not a stimulus for the 

 lateral-line organs. This is in agreement with Euchs's results ( L s: »4. p. 473) on the 

 vesicles of Savi which were stimulated by pressure hut not by heat. 



The reactions of Fundulus to heat, though of negative value so far as the pur- 

 poses of this paper are concerned, have an interesting biological hearing. It appears 

 from the experiments given that at a temperature of 19.5 C. (corresponding to that 

 of the outside water from which the animals had been taken), or at lower tempera- 

 tures down to 9 C. the fish remain, when otherwise undisturbed, near the top of the 

 water; but at temperatures above 19.5° ('.. particularly about 30 ('.. they seek the 

 deeper water and remain there. In other words, they are negatively geotropic in 

 the cooler water (9° to 19.5 ('.), and become positively geotropic in the warmer 

 water (25.5 C. to 30. .V C.), the increase of temperature causing a reversal of the 

 sense of geotropism. This change is just the opposite of that recently pointed out 

 by Torelle (1903. p. -175) for the frog. This animal remains near the surface of the 

 water at high temperatures, and goes to the bottom at low temperatures, the turning 

 point being at about 10 c C. Probably these reactions, though reversed in the two 

 instances, are not without significance for these two species. The frog may be thus 

 protected from severe cold and the lniunmichog from overheated surface water. 



Salinity. — Near the shore, and particularly near the mouths of rivers, the salinity 

 of the sea water is subject to much variation, and it is not impossible that differences 

 in this respect might be responded to by fishes through their lateral-line organs. 

 Tests in this direction were made upon Fundulus heteroclitus by subjecting normal 

 and cut individuals to the action of sea water variously diluted or concentrated. 

 The sea water at the end of the government wharf at the Woods Hole laboratory is 

 well mixed by the tides, and has the usual specific gravity of about 1.025. Water 

 taken from this source was diluted with tap water to decrease the salinity, or concen- 

 trated by boiling to increase it. Care was taken after the boiled water had been 

 cooled to aerate it thoroughly before it was used in experiments. 



Normal and cut fishes were placed first in glass jars containing ordinary sea 

 water and then in jars containing the diluted sea water. The fishes showed no char- 

 acteristic reactions to mixtures containing 90 per cent. 80 per cent, 70 per cent, or 

 60 per cent of sea water. In the mixture containing half sea water and half fresh 

 water a decided reaction was obtained in that the fishes swam about in an excited 

 way. often with darting movements, and were as frequently found in the deeper 

 water as near the top. Very slight evidence of this condition could at times be 

 detected in the 60 per cent and 70 per cent mixtures, but the reactions were most 

 decided in the 50 per cent mixture. Since the normal and the cut individuals were 

 indistinguishable in respect to these reactions, there was no reason to suppose that 

 the diminished salinity of the water was a stimulus for the lateral-line organ-. 



Both classes of fishes were put into sea water concentrated by boiling to three- 

 fourths its original volume (the specific gravity was something over 1.030). In this 

 water the fishes swam and respired normally, though it was evident that they were 

 buoyed up by the greater density. Normal and cut fishes were again indistinguish- 

 able, and there was therefore no reason to suppose that the increased density had any 



B. B. F. 1904—13 



