INSECT METAMORPHOSIS. 345 



answers to this question have been attained, according to my 

 view, by weighing fresh pupae. It appeared that the growth of 

 the caterpillars (the term of which was determined by the weight 

 of fresh chrysalids) underwent in all cases, without any exception, 

 a considerable retardation under the influence of thyroid feeding 

 (cf. Table III.). The differences between the control and the 

 experimental material are here always positive, in 3 cases being 

 biometrically very significant. The thyroid had therefore in this 

 respect an undoubtedly negative influence on the processes of 

 larval growth, i.e., the dosing of thyroid as well as the age of 

 the animals have been well chosen to demonstrate the supposed 

 influence of this substance. It is very characteristic that the 

 variability of weight of the "thyroid" caterpillars does not 

 undergo any essential and corresponding changes (cf. Table III.). 

 This points to the fact that the negative influence exerted here 

 by thyroid feeding on growth of caterpillars had the same qualita- 

 tive and quantitative effect for all animals. 



The influence of organic or even inorganic compounds of 

 iodine on amphibian metamorphosis is much discussed in recent 

 years and the problem contains certain discrepancies (cf., e.g., 

 the papers of Romeis, '18, Allen, '19, Hirschler, 'i8-'i9 and '22, 

 Huxley, '22, Huxley and Hogben, '22, Uhlenhuth, '22, and 

 others). Gedroyc ('23) studied the problem in respect to insects, 

 viz. on Deilephila etiphorbics L. In two experiments each con- 

 taining 5 "iodine" caterpillars, the author observed an accelera- 

 tion of the pupation of the experimental specimens relatively to 

 the 15 control caterpillars. On the contrary, in the third 

 analogous experiment in which also 5 animals, but 2 or 4 days 

 younger than the larvae of the preceding series, were used, the 

 larval period underwent in the "iodine" material even a certain 

 prolongation. Hence the inference of Gedroyc as to the decisive 

 influence of age and "state of growth" of the animals exerted 

 on the direction of the action of iodine. 



The material of Gedroyc being scanty I have studied anew 

 the problem of the influence of iodine on insect metamorphosis. 

 My experiments were performed on caterpillars of Pieris brassicce 

 L. Larvae hatched between August 2d and 3d were used in all 

 4 experiments. Cabbage leaves abundantly sprayed with Lugol's 



