344 STEFAN KOPEC. 



upon (cf., e.g., the manual of Biedl, '22, as well as the papers of 

 Romeis, 'i4-'i5, '16 and '18, Gedroyc, '23, Deutsch, '23, and 

 others). Consequently the absence of any considerable and 

 constant differences in the processes of metamorphosis between 

 my control animals and those fed on thyroid, does not solve our 

 problem. We ought to take into consideration, that owing to 

 individual fluctuations on the starting day of the thyroid feeding, 

 i.e. on June 5th, the larvae experimented upon without any doubt 

 differed from one another considerably both in regard to weight 

 and most probably also to stage of development, although having 

 hatched during one and the same night. It therefore was a 

 priori not known whether the average terms of metamorphosis 

 remained unchanged in spite of the different influence exerted by 

 thyroid on separate specimens. For instance, if the positive 

 and the negative influence exerted by thyroid feeding on separate 

 caterpillars were of identical intensity, the average duration of 

 the larval as well as of the pupal stage would remain unchanged. 

 The so to speak latent influence of thyroid feeding ought to be 

 noticeable here only by the variation of the terms of meta- 

 morphosis, as the range of individual fluctuations of the terms 

 of pupation and emergence of adult moths would in such case 

 undergo in the experimental materials a distinct widening. As 

 a matter of fact in my experiments no remarkable changes in 

 the coefficients of variability of these terms of the mentioned 

 variation may be seen (cf. Tables I. and II.). The differences 

 of the appertaining coefficients between control and thyroid 

 materials have opposite signs, in one case being positive, in the 

 remaining negative. The ratio of the difference between the 

 coefficients to its probable error was only in few cases larger 

 than 3, as a rule attaining from 0.2 to 2.3 only. It follows 

 therefrom that these biometrical tests show no distinct influence 

 of thyroid feeding on the rate of metamorphosis of the insects 

 experimented. 



The above results require a certain supplement in still another 

 direction. Viz: the question arises whether in these experiments 

 the lack of influence of thyroid on metamorphosis is caused by 

 too small quantities of the substance added, or unsuitable age of 

 the animals at the beginning of the experiments. Decisive 



