312 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



ature of the water in which it swims. Thus the dogfish {Squalus acan- 

 tliias, Liiinseus) possessing a far more perfect digestive and circiihitory 

 system than the cod, shows a much greater excess of blood temperature 

 above that of the surrounding water ; and cod taken at the depth of 15 

 fathoms in water at 52° F., show a less excess than others taken in 25 

 fathoms at lio, but a greater excess than bhie-fish [Pomatomus saltatrix 

 (Linn.) Grill) taken at the surface, at 69° and 70°, which is presumably 

 nearer the normal temi)erature of the last named fish. 



Upon this question of normal temperature, my observations have not 

 thrown much light, owing to the fact that nearly all the fishes observed 

 have come from water at about the same temperature, and that blue- 

 fish, from which the most valuable results were to be expected on 

 account of their acti\ity and the warmth of the water which they 

 inhabit, could not be taken with a line after the two days of their first 

 appearance. It is reasonable to suppose, from the fact that the cod, for 

 instance, shows a less difference when taken from warmer than from 

 cold water, that a point would soon be reached at which the tempera- 

 ture of the blood of the fish would coincide with that of the surrounding 

 water, and that this point would be near the "normal" for that family, 

 or in other words the limit above which it could not live.* 



The experiments are set forth at length in Table B, but some of the 

 conclusions for which tbey furnish a reasonable basis may be con- 

 veniently stated here, considering each species se]>arately. 



1. Gojy {Gadus morrJma^ljimiiidViS,). Twelve observations. The fishes 

 were taken with a hand-line, either at the edge of " Shank-Painter 

 Bar," a sand-bank about half a mile wide which makes out along the 

 end of Cape Cod from Race Point to Wood End light-house, in 22-25 

 fathoms of water, or on the " Ledge," a small rocky shoal lying about 

 seven miles WSW. from Wood End light, where there are from 13 to 

 15 fathoms of water, according to the state of the tide. The rectiun 

 showed an average excess of 0.97° above the temperature of the water 

 near the bottom. In the bloody fluid resulting from the mixture of 

 water with the blood escaping from the heart into the " thorax," the 

 average excess of temperature was 3°, and in the heart itself 4.63°. In 

 one instance an incision was made into the side of a very large cod, 

 from which arterial blood gushed forth. A thermometer plunged into 

 this incision showed only 1.5o excess over the temperature of the water 

 near the bottom. It was this observation which suggested the thought 

 that the venous blood might be warmer than the arterial. 



* Prof. G. Browne Goode, who has been investigating the question of the tempera- 

 tures preferred by ditfereut tishes, conchides that the cod and its congeners seek water 

 at 38° to 42° F. ; that the temperature range of menhaden lies between 50° and 75° ; 

 that blue-fish are rarely to be found in water below 40°, or mackerel below 45°; while 

 black bass {Mkropicrns) thrive in the water of the northern lakes, frozen over for 

 three months in the year and never rising above 65°. as well as in that of the Florida 

 rivers, which becomes as v/arm as 90° in summer. Different families, as thus appears, 

 show very different, powers of adaptation to extremes of temperature. 



