5IO ON INCREASE IN SIZE [pt. iii 



79, where the Hnear relationship clearly appears, and the velocity 

 increment is directly proportional to the temperature increment. In 

 1913-he continued this line of thought by finding that the eftect of 

 temperature on (a) the rate of segmentation in the frog's egg, {b) the 

 rate at which definite later developmental stages in the frog embryo 

 are reached, and {c) the hatching time of a water-beetle, Acilius 

 sulcatus, could in all these cases also be expressed by a straight line. 

 In the case of the frog, as Krogh pointed out, it would have been 

 absurd to express this linear relation in terms of Q^^q , for Q^^q would 

 thus become: 



and could hardly be said to be a constant if it was constantly 

 varying. Krogh did not compare his results with those of Hertwig, 

 for the latter used rather different technique, e.g. transferring 

 his embryos and eggs very slowly and by stages to the constant 

 temperature basins. This procedure Krogh did not find necessary, 

 though he observed that the limits of normal development are 

 narrower during the earlier stages than they are later. The linear 

 relationship thus found deviated, however, to some extent below 7°. 

 Exactly the same straight line was found when the velocities at 

 which later developmental stages were attained were plotted against 

 the temperature, though here divergence began as high as 12°. The 

 hatching time of the water-beetle eggs behaved in the same way. 

 Next Krogh took the figures of Loeb and Loeb & Wasteneys for 

 echinoderm eggs already mentioned, and found that they also were 



best expressed by a straight line when —. ; was plotted 



■^ ^ in mmutes 



against temperature. These results are all summed up in Table 71, 

 which gives the geometrical characters of the straight lines, i.e. their 

 slopes, together with other data about the embryos in question. In a 

 further paper Krogh showed that the relation between the tempera- 

 ture and the carbon dioxide production of the chrysalides of Tenebrio 

 molitor, the mealworm, could also be best expressed by a linear relation, 

 and was not susceptible of description by the van't Hoff formula. 



At this point the question became a matter of dispute concerning 

 the proper way of calculating the results obtained in such experi- 



