**» jparl of the Problem of Evolutioii. 65 



and how they have been kept up in tlie colder epochs which 

 have succeeded. 



11. — The chemical phenomena of life were at first mani- 

 fested under very high temperatures ; in addition to the proofs 

 furnished by a study of the flora I would add the following : — 

 The invertebrates, the first vertebrates, had a heat-producing 

 power which might be reckoned as nil, or, at least, very 

 feeble. Though they were animals of low chemical tempera- 

 ture, T consider that they confirm by this very absence (of 

 heat-producing power) the conditions of high temperature 

 under which tliey lived. A heat-producing capacity capable 

 of raising their temperature above that of the surrounding 

 medium was wanting, for the simple reason that there was no 

 need for it. 



Figures lend still further probability to this life at high 

 temperatures. The silkworm nurseries are kept at 40° ; the 

 tortoise can withstand a stove-heat of 40° ; Spallanzani and 

 Sonnerat have trained certain fish not only to live but to 

 reproduce their kind at 40°-44° ', M. Marey cites the case of 

 a Gymnotus which throve at 41° ; a python incubates at 41°'5 

 (Valenciennes) : all which temperatures would, as is known, 

 be rapidly fatal to man. 



These invertebrates and primary vertebrates in our day 

 lead but a very precarious life outside of the tropics. They 

 do not survive the first frosts of autumn or become torpid ; 

 the chemical phenomena of life are suspended, the venous 

 and arterial blood of the hibernating reptile become mingled. 

 Their very survival is to be explained by a modification of 

 their chemical processes ; in the laboratory, mammalian 

 pepsine is only active on food at a temperature of about 38°, 

 reptilian pepsine is still active at 0°. 



III. — The first animals lived, then, by the high temperature 

 which they received from their environment. What did life 

 become as this temperature fell ? Two logical hypotheses 

 present themselves : — 



A. Either life continued at the temperature of the sur- 

 rounding medium. In this case it modified the reactions of 

 its chemical phenomena and adapted them to the lower tempe- 

 tures (cold-blooded animals, reptilian pepsine). 



B. Or it attempted to maintain artificially the temperature 

 of its chemical phenomena, and to tliisend created for itself a 

 function which gave rise to the production of heat. In this 

 case life must always submit to the general law of adaptation 



Ann. & Mag. N. Hist. Ser. 6. Vol. xviii. 5 



