AND OF LIGHT. 



229 



5.2, and 4.9 times greater than at the highest tempera- 

 ture. In one plant, however, the temperature of 37.2 

 was sufficient to stop all growth, so that this was a 

 slightly supra-maximal temperature. 



That the increased growth produced by warmth leads, 

 at least in some cases, to an actual increase in the size 

 of an organism, is proved by some f urjther observations 

 of the author on Echinoid larvae. 'No special determina- 

 tions were made as to the effect of temperature on 

 growth, but it was noticed that, whilst at a temperature 

 of 13.8, the ova took about 22 hours to reach the free 

 swimming blastula stage, they took only about 5 hours 

 at 24. We may assume, then, that the rate of growth 

 increases rapidly with temperature. The effect of 

 various temperatures on the actual size of the larvae 

 may be gathered from the following table:* 



Larvae of three different species were allowed to develop 

 at four different temperatures, and measured after 8 

 days' growth in respect of both their body length and 

 their anal arm length, and this latter measurement was 

 calculated as a percentage on the former. In the case 



* Phil. Trans. 1898, B. p. 479. 



