24 Francois Bourliere 



During the twenties, Pearl (1928) and his associates were 

 nevertheless able to establish, by careful experiments, that the 

 lifespan of some invertebrates could be condensed or 

 lengthened as the average metabolic rate was raised or lowered. 

 Without considering all the details, it seems timely to recall 

 their main observations. MacArthur and Baillie (1929) kept 

 parthenogenetically produced Daphnia magna at various 

 temperatures, ranging from 8° to 28° C, the other conditions 

 remaining constant. In this way the duration of life of these 

 cladocerans varied widely, the mean lifespan being, on an 

 average, 25-5 days at 28° C as compared with 108-1 days at 

 8° C. At the same time they found that an acceleration of 

 metabolic rates was always associated with a nearly propor- 

 tionate decrease in duration of life. An elevation of tempera- 

 ture from 8° to 18° C increased the Daphnias' heart -rate by 412 

 per cent and their susceptibility to KCN by 435 per cent, 

 whereas it shortened their lifespan by 423 per cent. Similar 

 results were obtained in Japan by Terao and Tanaka (1930) on 

 another cladoceran, Moina macrocopa. 



Using the fruit fly, Drosophila melanogaster, Alpatov and 

 Pearl (1929) came to very similar conclusions when studying 

 the effect of the temperature, during development and 

 imaginal life, upon the duration of life of that insect. A high 

 temperature (28° C) during development shortens the duration 

 of the subsequent imaginal life at all temperatures and in both 

 sexes, with but one exception; e.g., females reared at 28° C 

 had a mean duration of life of 28 • 5 days, while those reared 

 at 18° C lived for 70-6 days. The effect of temperature during 

 the imaginal stage upon the duration of life of the imago itself 

 is equally striking; as the environmental temperature is 

 higher flies live, on an average, a shorter time. Similar 

 results have been obtained by Loeb and Northrop (1917). 



Another means of influencing the metabolic rate of inverte- 

 brates is food restriction. Using the two already mentioned 

 species of cladocerans, Ingle (1933) and Ingle, Wood and 

 Banta (1937) have found that Daphnia which are starved live, 

 on an average, about 40 per cent longer than those which are 



