DEVELOPMEN1 AND DURATION OF LIFE IN INSE< tS. 13 



lower or higher temperatures should be applied only to larvae, 

 the chrysalids being kept in normal conditions, might solve the 

 problem as to whether and to what degree the changed tempera- 

 lure has an influence not only on the celerity of metabolism, but 

 also on the -upposed function of the brain. 



The attempt- hitherto made to explain the metamorphosis <>t 

 in-ert- refer to the last stage of the processes. The appearance 

 of phagoi \ losis, of degeneration, of asphyxia and of other 

 'causes" of transformation is not yet elucidated. My experi- 

 ments on the function of the larval brain as well as the discovery 

 of tyrosinase in caterpillars and chrysalids made by Dewit/ 

 ''05 and '16) and confirmed by Steche and \Vaentig ('13) together 

 \\iih the present results on the starvation of caterpillars may 

 li ad to a better knowledge of the cause of insect metamorphosis. 

 Hut my "secretory" theory of metamorphosis will not be well 

 Lioimdcd until we succeed in finding in the structure of the brain 

 an adequate base for the theory, i.e.. until certain specific chai 

 in the brain not only during pupation, but also during moult- 

 \\ill ha\e been ascertained. A great support might be .iltunled 

 by positive experimental results on transplantation of brains, or 

 on injections of extracts of this organ into brainless specimens. 

 The latter experiments only would be able to dispel every doubt 

 in regard to the validity of my previous conclusion that the in- 

 dubitable influence of the brain on metamorphosis is due to an 

 internal secretion of this organ. 



I Vrgrncr ('09) lastly considers the imaginal form to be ph\ 1 . 

 netii-ally older than the larval form, which developed -v ( .mlarily 

 In 'in the hilly developed insect owing to numerou- -n-ondary 

 life conditions "unter fortgehender Ketanlation der I ait\\ i( klung 

 imaginaler Organe" (p. Ii). I think that my experiments of 

 series B distinctly prove that in n< >rmal cirrmn-i .m< - the devel- 

 opment of the imaginal discs is retarded during larval stages. 

 I cannot deny that in the light of these re-ults the supposed 

 retardation of the development of the imaginal organs gains an 

 experimental base, at lea-t in ontogriu-tii- evolution. 



3. INANITION AND Ci KIAIN I'KMM i \is OF GROWTH. 



In this chapter I take into account only the final stages of 

 growth of caterpillars c\pre--rd by the \\eiglit of new-formed 



