PHYSIOLOGY OF CHROMATOPHORES OF FISHES 537 



pressure of the blood following the action of the hyper- and hypo- 

 tonic media. The dilute sea-water he believes to approximate 

 the A of F. heteroclitus to a degree which renders it harmless. 

 From these experiments of Garrey's it is clear that the scales 

 are essential to the life of the fish even in sea-water. From the 

 experiments with individual scales in distilled water it seems that 

 not the scale but the epidermis is essentially what protects the 

 fish from the sea- or fresh-water.^ 



Since the migration of the melanin granules in sea-water is 

 practically nil and since there is always a definite response to 

 distilled water, the question naturally followed as to the nature 

 of the inhibiting factor in sea-water which prevents the contrac- 

 tion that invariably occurs in distilled water. Further experi- 

 ments were carried out with sea- water from other sources/ 

 and, whereas these showed a somewhat greater initial expansion, 

 though not so great as in the melanophores of a normally dark 

 fish, a contraction never followed. 



A combination of the two types of experiments was now tried. 

 Scales were immersed in sea-water diluted with distilled water 

 in varying proportions in order to eliminate the concentration 

 factor. The following relationships were brought out. 



1. When the dilution was slight, 3 parts sea-water: 1 distilled 

 water, a somewhat greater expansion occurred than in the control 

 scales in sea- water but this was not so great as in the case of 

 normal, dark fish. 



^ This fact may throw some light upon the recent controversy concerning the 

 possibility of keeping F. heteroclitus alive in fre^ water. Obviously fish which 

 showed missing scales would be discarded in such experiments. However, it 

 would be very difficult to determine casually whether or not portions of the epi- 

 dermis had been rubbed off. This occurs very easily especially if the fish are caught 

 in a seine. It follows therefore that the discrepancies in these experiments in 

 keeping the fish alive in fresh water may have been due to a more or less perfect 

 condition of the epidermis. Scott ('11) has suggested a different explanation 

 for Garrey's results. 



* The sea-water in these experiments was taken from the taps at the Wood's 

 Hole laboratories (U. S. Fisheries and Marine Biological) and at flood tide at Cape 

 May Point, N. J. This was all slightly more dilute than that of the first seawater 

 experiments which had become somewhat concentrated by evaporation. No freez- 

 ing-point determinations were made. 



