962 ENERGETICS AND ENERGY-SOURCES [pt. iii 



with morphological events, namely, the difficulty of classifying mor- 

 phological events in a really satisfactory way. In spite of all that had 

 been done on metamorphosis by histologists, zoologists and naturalists, 

 Tangl could not with certainty decide in what proportion growth 

 and differentiation were proceeding ; terms vague enough at best, and 

 presenting almost equal difficulties in embryonic life. We here come 

 face to face once more with that great impediment to research in 

 these domains, the fact that we have no quantitative measure of 

 differentiation (on this see Section 3-2 and the Epilegomena) . 



Before discussing the general outcome of Tangl's work, the eighth 

 paper of his series must be mentioned. In it Glaser reported his 

 estimations of the calorific value of the egg of a teleost, the minnow 

 Fundulus heteroclitus. The figures came out as follows : 



calories 



1000 eggs 3273 



1000 embryos ( + membranes) ... 2550 



723 



As 1000 finished embryos weighed 0-535 gm. dry, the S.Ea. was 

 1350 cal. Glaser, however, realising that sHghtly more than half the 

 weight of the embryo at hatching was unused yolk, doubled this 

 figure, obtained an estimate of 3280, which was in good agreement 

 with the rest of the figures obtained by Tangl and his school. Glaser 

 also calculated that the specific energy-content of the substance 

 burnt was 9-0 Cal., from which he concluded that the greater part 

 of it was fat. 



7-3. The Relation between Energy Lost and Energy Stored 



Subsequent work by various authors brought forward figures which 

 are shown in Table 121, but which do not agree with those of Tangl 

 and his associates. This is probably due to the less accurate character 

 of the later work. For the frog the figures of Faure-Fremiet & Dragoiu, 

 as can be seen from the table, differ somewhat from Tangl's, especially 

 as regards R.Ea. and S.Ea., although the efficiency as calculated 

 from them agrees well enough with the earlier work on the silkworm 

 and the chick. This cannot be said of Faure-Fremiet's experiments on 

 the eggs of Sabellaria and Ascaris. Perhaps the divergence here is partly 

 due to the difficulty in deciding just when embryonic development is 

 complete, and the impossibility of separating the embryo from the 

 yolk. Faure-Fremiet's high levels of efficiency are probably illusory. 



