230 THE RATE OF GROWTH fcH. 



These values are not only concordant, but are of the same order 

 of magnitude as the temperature-coefficient in ordinary chemical 

 reactions. Peter has also discovered the interesting fact that the 

 temperature-coefficient alters with age, usually but not always 

 decreasing as time goes on*: 



Sphaerechinus Segmentation Q^q =2-29 Q^ = 1-09 

 Later stages 2-03 1-07 



Echinus Segmentation 2-30 1-09 



Later stages 2-08 1-08 



Rana Segmentation 2-23 1-08 



Later stages 3-34 1-13 



Furthermore, the temperature-coefficient varies with the tem- 

 perature itself, falhng as the temperature rises — a rule which Van't 

 Hoff shewed to hold in ordinary chemical operations. Thus in Rana 

 the temperature-coefficient (Qiq) at low temperatures may be as 

 high as 5-6; which is just another way of saying that at low 

 temperatures development is exceptionally retarded. 



As the several stages of development are accelerated by warmth, 

 so is the duration of each and all, and of life itself, proportionately 

 curtailed. The span of life itself may have its temperature- 

 coefficient — in so far as Life is a chemical process, and Death a 

 chemical result. In hot climates puberty comes early, and old age 

 (at least in women) follows soon; fishes grow faster and spawn 

 earlier in the Mediterranean than in the North Sea. Jacques Loeb f 

 found (in complete agreement with the general case) that the larval 

 stages of a fly are abbreviated by rise of temperature; that the 

 mean duration of life at various temperatures can be expressed by 

 a temperature-coefficient of the usual order of magnitude ; that this 

 coefficient tends, as usual, to fall as the temperature rises; and 

 lastly — what is not a little curious — ^that the coefficient is very much 

 the same, in fact all but identical, for the larva, pupa and imago of 

 the fly. 



* The diflferences are, after all, of small order of magnitude, as is all the better 

 seen when we reduce the ten-degree to one-degree coefficients. 



t J- Loeb and Northrop, On the influence of food and temperature upon the 

 duration of life, Journ. Biol Chemistry, xxxii, pp. 103-121, 1917. 



