684 THE RESPIRATION AND [pt. iii 



unimportant, and the fundamental waves of metabolism, growth, and 

 differentiation, may pass through the individual organism without 

 paying much attention to it. Secondly, although it is our duty to 

 regard as many kinds of embryo as possible as special cases only of 

 a few profound and general rules, we cannot escape the fact that 

 their origin is very different, and it may not at present be possible 

 to speak of holoblastic and meroblastic eggs, for instance, on the 

 same basis. Thus the anomalous case of Ascaris eggs, in which there 

 is no rise of metabolic rate during segmentation, etc., must be 

 remembered. I shall return to these questions at the end of this 

 section, when the data for the bird and the mammal have been 

 presented. 



Gayda's curve shows that shortly after fertilisation i gm. of 

 toad embryo liberates 0-037 §"^- cal. per hour, while at hatching 

 it liberates about 0-30 gm. cal. per hour, and at its maximum 

 (20th day after fertilisation) it liberates as much as 0-97 gm. cal. 

 per hour. Gayda did not himself calculate any calorific quotients, 

 for he did not himself make any estimations of oxygen uptake, 

 nor had at that time Parnas & Krasinska's work on amphibian 

 embryos been published. Unfortunately, although they worked with 

 Bufo vulgaris, none of their published protocols refer to that organism, 

 but all to Rana temporaria and Rana esculenta. It is therefore not 

 possible to put the figures together. The total amount of heat given 

 out by I gm. of embryo (wet weight) throughout the embryonic 

 period (fertilisation to hatching) was 30-276 gm. cal., and the cor- 

 responding quantity for i embryo was 0-1207. These values are the 

 " Entwicklungsarbeit " of Tangl, relative and simple respectively (see 

 p. 950). Gayda pointed out that the figure of about 30 gm. cal. 

 was not nearly so great as the corresponding values for the chick 

 found by Tangl & von Mituch, and for the silkworm by Tangl & 

 Farkas, of about 900 gm. cal., but, on the other hand, it was 

 about equal to Faure-Fremiet's figure for Sabellaria alveolata. These 

 questions of energetics will be dealt with fully in the section on that 

 subject. Between hatching and the end of metamorphosis 1668 gm. 

 cal. were given out per gram wet weight, and 67 gm. cal. per larva. 

 This covered 123 days. Thus the average heat output per gram wet 

 weight per day before hatching was 3-75 gm. cal., and the average 

 afterwards was 13-58, a striking result of the peak which occurs after 

 hatching. 



