96o ENERGETICS AND ENERGY-SOURCES [pt. iii 



metamorphosis, i.e. from complete pupation to free imago, had an 

 R.Ea. and an S.Ea. of about half the value for pupation plus metamor- 

 phosis, and, more significantly, half that for embryonic development. 

 As, in Tangl's belief, metamorphosis consisted only of "Neubil- 

 dungsarbeit" with very little "Wachstumsarbeit", the conclusion 

 naturally followed that the partition between the two was probably 

 50 per cent. Inspection of Table 121 shows clearly that, for the 

 formation of a gram of dry weight of finished embryo, an approxi- 

 mately equal amount of energy has to be used up, and this irrespective 

 of the position of the animal in the taxonomic scale. Tangl's remark 

 that "die spezifische Entwicklungsarbeit der tierischen Organismen 

 keine Funktion ihrer phylogenetischen Stellung und Organisation- 

 stufe ist" may be said to be true, though, in spite of the remarkable 

 correspondence between the silkworm and the chick, it would be 

 desirable to extend the number of well-authenticated cases. Tangl 

 also laid much emphasis on the fact that the energy utilisation was 

 much faster in embryonic development than in metamorphosis, in 

 the case of the silkworm, for instance, being as 2-97 : o-6i, or per day 

 per gram 198 cal, in embryonic life and 33 in metamorphosis. "Die 

 embryonale Entwicklung", said Tangl, "beansprucht also einen viel 

 grosseren und intensiveren Umsatz von chemischer Energie als die 

 Metamorphose; sie erfordert eine grossere und intensivere Arbeit." 

 Tangl admitted that an unknown proportion of his "Entwicklungs- 

 arbeit" in embryonic development and his " Umbildungsarbeit " 

 in metamorphosis was really "Erhaltungsarbeit", "energie d'entre- 

 tien", or maintenance catabolism, but he thought it possible that this 

 fraction was identical in the two processes. Thus the way was laid 

 open for the subtraction of the metamorphosis S.Ea. from the em- 

 bryonic S.Ea. He himself never actually made this calculation, but 

 it was obvious from his figures that the average values for metamor- 

 phosis were R.Ea. 437 and S.Ea. 1550 cal., while those for complete 

 development, when halved, were R.Ea. 422 and S.Ea. 1270 cal. 

 The energy of development, then, would be regarded as being 

 approximately equally divided between diflferentiation and growth- 

 processes. Tangl did not, however, by any means commit himself to 

 this conclusion, for he also suggested that the main component of 

 the energy burned during metamorphosis was "Erhaltungsarbeit". 

 At this point, indeed, Tangl and his associates came up against the 

 difficulty which so often confronts those who try to relate chemical 



