12 STEFAN KOPEC. 



is decreased, owing to its lowered function. The starved chry- 

 salids therefore begin their pupal stum* when the discs are better 

 developed and this causes acceleration of the development of the 

 imaginal body and hence abbreviation of the pupal life. 



The assumption that the larval brain exerts two different in- 

 fluences is neither astonishing nor incomprehensible in respect 

 to the well-known data concerning the physiology of organs of 

 internal secretion. The final development of the imaginal discs 

 and their definitive differentiation sets in before pupation or even 

 in the pupa, i.e., at a time when almost all larval tissues are un- 

 dergoing histolysis or have undergone it. Therefore it ought to 

 be admitted that during this period the influence of the brain 

 hindering the development of embryonal discs normally becomes 

 annuled by certain processes which are unknown to us. It is very 

 probable that the development of imaginal discs and the histolysis 

 of the larval tissues become, at least towards the end of larval 

 life, physiologically correlated with each other. In the contrary 

 case it could be hardly understood why the caterpillars deprived 

 of their brain the seventh day after their last moult do not, it is 

 true, exhibit any histolytical changes in their tissues, but the 

 imaginal discs contained in their body do not undergo final 

 growth and differentiation. (Kopec, '17 and '22 c). Indeed, 

 if there were no such correlation, the imaginal discs of the cater- 

 pillars deprived in that period of their brain (and therefore of 

 the organ retarding their evolution) ought to develop the organs 

 of the imago in spite of the absence of histolytical procesM-s in 

 the larval body. 



In contrast to my experiments on the starvation of caterpillars, 

 Loeb and Northrop ('17) have lately convinced themselves that 

 each of the separate stages of life in Drosophila occurs more 

 slowly in lower temperature and more quickly in higher ones. 

 The changes of temperature were applied by the mentioned 

 authors during the whole development of the animals, while in 

 my experiments the factor of inanition had a direct influence only 

 on the processes taking place in caterpillars, as the chrysalis 

 do^ not take food in normal conditions either. Loeb and Northrop 

 obtained the same changes of the duration of the larval and of 

 the pupal stage first of all owing to changed celerity of metab- 

 olism in the larva as well as in the pupa. Experiments in which 



