910 



GENERAL METABOLISM 



[PT. Ill 



Hatching 



Fig. 243. 



absorbed by the larvae, though the time they took to absorb a definite 

 amount was, of course, made longer or shorter. The effect of rising 

 temperature on the unfertilised eggs was to increase the permeability 

 of their membranes to water, so that, for instance, at 10°, an egg in a 

 definite period would increase its volume by 0-05 c.mm., and at 20° 

 by 0-28 c.mm. But the possibihty that the increase with temperature 

 was really due to the production of an unusually large amount of 

 osmotically active substances in 

 the egg-protoplasm was not ex- 

 cluded. Bialascewicz argued that 

 as the permeability to water is 

 increased five times by a rise of 

 temperature of 10°, and as the 

 development rate is increased 

 only two and a half times, one 

 would expect to find more water 

 in larvae brought up at 20° than 

 at 10°. Since experimentally this 

 was not the case, Bialascewicz concluded that the permeability of the 

 membranes to water was not the determining factor in the absorption 

 of water during amphibian embryonic growth. 



Galloway, inspired by Davenport's early work, also made a study 

 of the effect of temperature upon the absorption of water by the 

 developing frog larva. The embryos of Rana sylvestris, Amblystoma 

 punctatum and Bufo americana were subjected to temperatures varying 

 from 6° to 25°, and the water-content estimated from time to time. 

 The results obtained are shown plotted in Fig. 243, whence it can 

 readily be seen that the warmer the environment, the more rapidly 

 did the imbibition of water go on. But Galloway found that at 

 higher temperatures the final amount of water in the body was 

 slightly more than that at lower temperatures although the develop- 

 mental process up to the point when 75 per cent, water was reached 

 was not so much retarded by lower temperature as the stage 

 representing the maximum percentage of water. (See Table 107.) 

 The effects of temperature, therefore, were more marked on the 

 second phase of the process than on the first. In the first stage, 

 assimilation of yolk and cell-division is prominent, in the second 

 stage, assimilation of water. This is in exact accord with the finding 

 of Bialascewicz, for a period in which imbibition of water is 



