SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 687 



but his data at different temperatures are hardly sufficient to allow 

 of the calculation of a temperature characteristic. The total quantity 

 of heat lost, however, remained quite constant during periods of 

 doubling of weight at all temperatures at which normal develop- 

 ment proceeded; a finding which was later to be confirmed very 

 fully on the frog by Barthelemy & Bonnet using bomb calorimetric 

 methods, as will be related in the section on energy changes in 

 embryos. Gayda had expected that he would find the total amount 

 of heat given out to be the same at all temperatures, for, as Chambers 

 and Terni had shown, the amount of growth in frog larvae was the 

 same, only metamorphosis supervened earlier at the higher tem- 

 peratures than at the lower ones. Finally, Gayda compared the 

 heat production of the eggs with adult frogs. The latter evolve 

 0-45 gm. cal. per hour per gram on an average, as against the 

 maximum of 0-98 gm. cal. per hour per gram at the 20th day from 

 fertilisation. 



4-9. Respiration of Insect Embryos 



The first organism of this kind which was examined was the silk- 

 worm, Bomhyx mori. Apart from early work by Duclaux, the first 

 papers were those of Luciani and Luciani & Piutti, who estimated 

 quantitatively the gaseous exchange of the eggs. The silkworm embryo 

 has a complicated course to pursue, for the egg is laid in the late 

 summer or autumn, and the first week after fertilisation is passed 

 before the hibernation period can be said to have begun. During 

 this time the colour changes from pale yellow to greyish brown. 

 Throughout the winter the egg remains in a sort of latent state, but 

 when the spring begins the developmental process is suddenly released, 

 and 1 1-14 days are sufficient for hatching. A similar quiescent period 

 or "diapause" is observable in grasshoppers and may be shortened 

 or lengthened, according to Bodine, by raising or lowering the 

 temperature. At high temperatures the quiescent period may only 

 be represented by a trough but it cannot be abolished altogether^. 



Luciani & Piutti were not able to confirm the preliminary results 

 of Luciani himself, that during the hibernatory period the eggs could 

 li\ e without oxygen, but found instead that the respiration at that 

 time was directly proportional to the partial pressure of oxygen. 



^ Conditions in orthopteran development are rather complicated, and for the details 

 reference should be made to the memoirs of Bodine. Respiratory Quotients of 07 to 0-8 

 seem to be usual in this material. 



