IO STEFAN KOPEC. 



the seventh day after their last moult underwent pupation in three 

 different broods after from 7 to 13, from 7 to 16 and from 7 to 

 15 days (or on the average after 10.6, 10.8 and 10.0 days), 

 whereas the control specimens of these broods become chrysalids 

 as early as after from 6 to 12, from (> to 12 and from 5 to 12 days 

 (or on the average after 8.2, 9.3 and 8.6 days). On the contrary 

 the larval life of the females of the same broods in which starva- 

 tion began approximately from the tenth day after the last moult 

 was much shorter than that of control larvae, as pupation occurred 

 here from 4 to 8, from 5 to 8 and from 4 to 8 days (or on the aver- 

 age after 5.5, 6.6 and 6.8 days), in control specimens from 5 to 

 10, from 6 to 10 and from 7 to 9 days (or on the average after 

 7.4, 7.6 and 8.1 days). Hence follows: (i) The character of the 

 influence, whether accelerating or retarding, exerted by starva- 

 tion on the processes of metamorphosis depends on the period 

 of life or the developmental stage on which the factor begins. (2) 

 This moment may be accurately determined by means of ex- 

 periment, vi/, in the females of Lymantria dispar L. In nix- 

 cultures the critical moment during which the influence of in- 

 anition delaying metamorphosis is changed into an accelerating 

 one fell on the period between approximately the seventh and the 

 tenth day after the last moult. 



An essential explanation of such different behavior of cater- 

 pillars may be found in my former studies on the importance of 

 the brain for insert metamorphosis (Kopec, '17 and *22r). It 

 was shown that the female caterpillars of this moth, deprived ot 

 brain the seventh day after their last moult, live far longer than 

 control animals, but they die without undergoing transforma- 

 tion. On the other hand, the removal of the brain from rater- 

 pillars the tenth day after their last moult has no influence either 

 on the processes of pupation or on the emergence of moths. 

 From various experiments supported by observation on control 

 material it follows that the brain plays here most probably the 

 role of an organ of internal secretion. From these results we may 

 infer that by depriving caterpillars of food since the tenth day 

 after their last moult we afford exceptionally favorable condi- 

 tions for metamorphosis, viz, the substance or substances al- 

 ready produced by the brain in sufficient quantities lind in such 

 starved organisms less material which ought to be transformed 



