HABITATS 43 



work is simply physiology applied to natural phe- 

 nomena ; it is an attempt to explain in physiological 

 (i.e. physico-chemical) terms the reactions of animals 

 to ecological conditions. Attempts to obtain simple 

 mathematical formulae for the temperature co- 

 efficients applicable to such experiments on animals 

 have not so far been successful. The work of 

 McLagan (1932) suggests one reason for this failure. 

 He worked on the spring tail {Smynthurus viridis) 

 and found that different processes in the life of the 

 springtail had different temperature and moisture 

 optima. In other words, such an insect could find 

 no environment to which it was completely adapted, 

 and any attempt to express the temperature-humidity 

 reactions in one formula would fail owing to hetero- 

 geneity of the processes abstracted. 



Much of the laboratory technique has consisted of 

 attempts to produce in the laboratory constant 

 temperatures, constant humidities — in fact, artificially 

 constant climates. It is, however, realized by most 

 experimenters that these conditions do not accurately 

 reflect the sort of climatic complexes found in nature. 

 CHmate is always fluctuating, and it remains to be 

 discovered just how far the effects of a constant 

 temperature or humidity on an animal approximate 

 to those produced by a fluctuating environment with 

 an average temperature or humidity of the same 

 amount. 



The dimograph (invented by Ball in 1910 and 

 named by Taylor in 1916) is a method of combining 

 experimental data and field observations. It con- 

 sists of a contoured diagram of the type already 

 mentioned, expressing the combined effects of 

 temperature and humidity (or other moisture index), 

 and based upon the meteorological conditions occur- 

 ring within the range of the animal studied. This 

 diagram is then compared with the experimental 

 data. The comparison makes it possible to find out 

 whether an insect pest is already living within the 



