352 STEFAN KOPEC. 



ating influence on metamorphosis may thus have annulled in 

 the case from my paper of 1922 the hindering influence of 

 starvation. In other words, probably owing to mutual counter- 

 action of the two opposite influences the normal term of pupation 

 was maintained here. 



From the foregoing inquiry the following summary may be 

 given : 



i. The administration of thyroid to caterpillars of Lymantria 

 dispar L. did not cause any distinct changes in the duration of 

 the larval nor of the pupal period. The only effect was a distinct 

 diminution of the weight of the chrysalids. 



2.' Neither the variability of the pupation term, nor that of 

 the emergence of the moths, nor of the pupal weight underwent 

 any regular or essential changes as compared with corresponding 

 items of the control materials. 



3. Lugols' solution (IK + I) had no distinct influence on the 

 rate of pupation of the caterpillars of Pieris brassicce L. and its 

 only consequence was the negative changes of pupal weight. 

 In respect to the scanty material these experiments are however 

 not considered as decisive. 



4. Negative correlation between the growth of caterpillars of 

 Lymantria dispar L. (the growth being expressed as weight of 

 the pupae) and the duration of larval life cannot always be 

 observed. This fact as well as the diminution of growth in 

 spite of the unaltered rate of metamorphosis in the "thyroid" 

 experiments point to phenomena of concommitance but not of 

 functional correlation normally existing between metamorphosis 

 and growth of insects. 



5. The mortality of the " thyroid " as well as of the "iodine" 

 specimens was not larger than in the control materials. 



6. The hypothesis formerly uttered by the author as to the 

 hormonal influence exerted by the brain on insect metamorphosis 

 is by no means abolished by the negative results of the present 

 experiments. Neither is this hypothesis cancelled by the experi- 

 ments and considerations of Gedroyc. 



