SECT. 2] 



AND WEIGHT 



511 



ments, Kanitz contested the truth of Krogh's view that the van't 

 HofF equation was inapphcable, on the grounds that the straight 

 Hnes might be the result of two or three flat exponential curves. 

 (Kanitz seems not to have avoided confusion between the time taken 

 for development and the reciprocal of the time taken.) Kanitz 

 plotted the log. of the velocity (log 1000/^) against the temperature, 

 and obtained two straight lines in each case, just as Crozier did 

 afterwards, with kinks between 10 and 15°. He assumed therefore 

 that the Arrhenius formtila could be used and calculated Q^^q from it. 



Table 7 1 . Effect of temperature on embryonic development. 



Krogh's figures; 



Embryo 



Cod (Gadus morrhua 



and aeglifinus) 

 Plaice {Pleuronectes 



platessa) 

 Cod {Gadus merlangus) 

 Plaice {Pleuronectes flesus) 



„ {Pleuronectes 



platessa) 

 Sea-urchin {Strongylo- 



centrotus purpuratus) 

 Frog {Rana butyrhina) 



>J 5! 



Water- beetle {Acilius 



sulcatus) 

 Sea-urchin {Arbacia) 



Kraf ka in 19 1 9 found that in Drosophila the effect of temperature 

 on rate of development could be expressed best by a straight line, 

 but its effect on eye-facet number could be expressed best by an 

 exponential curve. The appearance of both forms in one and the 

 same living material made it unlikely that either relation needed 

 correction. It was more probable that the formulae themselves were 

 inadequate for proper analysis. Other lines of approach were made 

 by entomologists on the one hand and by marine biologists on the 

 other. Thus Reibisch worked over the original results of Dannevig, 

 and concluded that a certain amount of heat was necessary for 

 development and had to be supplied from outside, forgetting that 



[uj LIBRARY 



