SECT. 7] OF EMBRYONIC DEVELOPMENT 957 



phosis. Here he distinguished between "Erhaltungsarbeit" or basal 

 cataboHsm, i.e. energy of maintenance, on the one hand, and 

 "Arbeit fiir Bildung von lebenden Substanz", on the other hand, 

 but he regarded the former as negHgibly small during embryonic 

 development, probably a rather important error. The "Bildungs- 

 arbeit" he divided into " Neubildungsarbeit " and "Wachstums- 

 arbeit". Roughly corresponding to differentiation and growth 

 respectively, these terms stood for the production of organs and the 

 laying down of morphological and chemical structures in an archi- 

 tectural plan, on the one hand, and the actual increase in size of 

 individual cells and the body as a whole, on the other hand. Tangl 

 hit upon an ingenious method which he hoped would solve the 

 problem of assessing how much of the " Entwicklungsarbeit " was 

 devoted to "Neubildungsarbeit", and how much to "Wachstums- 

 arbeit", i.e. the study of insect metamorphosis. There, Tangl 

 argued, the weight loss was very slight, practically negligible, no 

 food was taken in, there would be no "Wachstumsarbeit" (Wa.), 

 and all the changes could be regarded as the rearrangement of a 

 pre-existent pattern, alterations of the form and spatial arrangement 

 of the cells making up the various organs. Everything would be 

 "Neubildungsarbeit" (Na.). This proposal, interesting as it was, was 

 from the first open to criticism. It was well known that the pupa 

 has a definite, if feeble, respiration, and therefore could hardly be 

 considered as losing no weight. Moreover, Tangl's calculation de- 

 pended upon the assumption not only that 



Ea. = Wa. + Na., 



which is probably not true, but also upon the assumption that the 

 " Umbildungsarbeit " (Ua., i.e. transformation work) of metamor- 

 phosis was equivalent to the Na. In other words, practically no 

 attention was paid by Tangl to the histolysis of the old arrangements, 

 although he was expressly studying a holometabolic insect. Why 

 should there not be a " Histolysearbeit " (Ha.)? It is well known to 

 builders and contractors that "Histolysearbeit" may be consider- 

 able. If there were, Ua. would be equivalent to Ha. + Na., and, 

 as no method was devised for distinguishing between these two, 

 the subtraction of Na. from Ea. to get Wa. was invalid. Again, the 

 insect larva and pupa contains a "fat body" which, according to 

 Folsom and many entomologists, can be considered as the equivalent 



