380 SCIENCE PROGRESS. 



table may be roughly divided into two classes. The first 

 seven of them are transparent pelagic animals, in which the 

 temperature increment is, with one exception, 3*2 and 

 upwards, and the percentage of solids in the tissues "6 per cent, 

 or less. The remainder, also with one exception, viz., Tethys, 

 are littoral animals, and not transparent, have a temperature 

 increment varying from 1*9 to 27, and contain from 117 

 to 22*3 per cent, of solids. In any case, whether the increased 

 resistance to temperature change be ascribed to the one 

 factor or the other, it is evident that there has taken 

 place an evolution of this physiological characteristic, and 

 that it has, at least to some extent, proceeded hand in hand 

 with the morphological evolution. 



In the above-mentioned animals, the respiratory activity 

 appeared to increase regularly with the temperature, and 

 there was no evidence that the nervous system had any 

 special power of influencing the metabolism. It has also 

 been hitherto generally considered that this is true for all 

 cold-blooded animals, and that, provided these are in a state 

 of rest, their metabolism and body temperature depend onlv 

 on the temperature of their surroundings. As a matter of 

 fact, the few data available did not altogether warrant this 

 conclusion. Thus Moleschott 1 found the carbonic acid out- 

 put of frogs at 5° to be in some cases greater than that at 

 io° and 1 5 . Also Schultz,'- in his determinations of the 

 carbonic acid discharge of the edible frog, Rana esculenta, 

 found the metabolism at 14-4° to be less than that at 6-4°. 



The writer 3 has recently made similar determinations of 

 the relations of the respiratory activity to temperature in 

 various amphibia and other cold-blooded animals, and has 

 found that in hardly any case does the carbonic acid output 

 increase regularly with increase of temperature. There 

 exist temperature intervals over which the metabolism 

 remains either constant, or varies but slightly. The animals 

 were slowly warmed from 2 to 30 , or slowly cooled from 

 30 to 2 , and the carbonic acid discharge determined over 



1 U?itersuchungen zur Naturlehre, 1857, Bd. ii., 315. 



2 Pfliigers Archiv, xiv., 78. 



3 J. Physio/., xvii., p. 277, 1894, and xxi., p. 443, 1897. 



