512 



ON INCREASE IN SIZE 



[PT, III 



no matter how hot the environment, the egg gets all its energy 

 for development from the inside. Apstein, who noted with Krogh 

 that the time/temperature relation was linear, i.e. the product was 

 a constant, formulated another "day-degree theory", which, how- 

 ever, was no improvement. On the Reibisch-Apstein view, a certain 

 sum of heat, a certain number of temperature units or day-degrees, 

 is necessary to complete embryonic growth. Thus if an embryo 

 hatches after lo days at 12° 120 day-degrees would be said to have 

 been required, so that at 6° 20 days would be required. Krogh & 

 Johansen were easily able to show the superficiality of such a treat- 

 ment. 



Williamson's experiments with herring, haddock and plaice eggs 

 also seem to show a linear 

 time/temperature relation, but 

 the variations are large. Elm- 

 hirst studied the hatching time 

 of Leander squilla and the de- 

 velopment of various decapod 

 Crustacea, and observed a con- 

 stant time/temperature factor. 

 He also went over the large 

 number of fragmentary papers 

 on the effect of temperature on 

 the development of fishes which 

 exist in the literature, mostly 

 in Fishery Board Reports, and 

 in many cases, though not in 

 all, succeeded in finding evidences of the Krogh straight-line relation- 

 ship between velocity and temperature. He thought that this emerged 

 more clearly if i -9° were added on to each temperature in order to have 

 the freezing-point of sea water as a basis. But, on the other hand, 

 in many cases, such as that of the cod (Fig. 80, taken from Fulton 

 from various official Reports) the time/temperature curve could cer- 

 tainly be said to have a temperature coefficient (2-3 for 10-20° 

 and 3-5 for 0-10°). Blunk working on Dytiscus embryos, and Blunk 

 & Janisch working on those of Blitophaga opaca, obtained straight 

 lines like Elmhirst for velocity/temperature graphs, i.e. hyperbolas 

 for time/temperature graphs. 



Sanderson has reviewed the work that has been done on the 



Fig. 80. 



