340 STEFAN KOPEC. 



Similarly, we cannot, according to my view, consider as decisive 

 the results obtained by Kahn who relies on 16 Tenebrio larvae 

 of which 6 were kept without any food, and every two specimens 

 from the remaining 10 were fed differently (fresh meat, fresh 

 thyroid, dried thyroid, meal and " Jodalbacid"). The experi- 

 ments of the same author on Corethra and Ecdyurus were made 

 on specimens collected in natural waters and therefore on 

 genetically totally unknown materials. Similar relations are 

 often met with also in other problems referring to the glands 

 of internal secretion. In these cases genetically homogeneous 

 animals used for the experiments and statistical elaboration of 

 adequate data, would, according to my opinion, contribute to 

 set aside numerous discrepancies. 



My experiments have been made on caterpillars from 4 lots 

 of eggs of Lymantria dispar L. deriving from 4 brother-sister 

 matings of moths belonging to the same pedigree and reared by 

 the author for several years. In order to deal with materials 

 homogeneous also in respect to age, I selected exclusively cater- 

 pillars which hatched during the night between April 2/th and 

 28th. On June 5th the thoroughly mixed caterpillars of each 

 lot were divided at random in two parts, one of which served as 

 control, the other being fed on leaves with thyroid. Fresh 

 willow twigs were accurately sprinkled with water solution of 

 the 'Tablettae thyreoideae" from the factory of "Gedeon 

 Richter' in Budapest. Ca. 450 experimental caterpillars re- 

 ceived daily: in the beginning 2, from June I2th 3, from June 

 i8th 4 tabloids, equal to i.o, 1.5 and 2.0 grams respectively of 

 fresh gland. (The efficacy of the preparation had been pre- 

 viously tested on tadpoles of Rana temporaria.} The control 

 animals were fed on willow twigs of the same species, sprinkled 

 with pure water. In both cases the leaves were administered 

 daily (after the superfluous water had been dried) in slight 

 excess of requirements, so that the whole food was almost totally 

 consumed by the next day. The thyroid-fed caterpillars took 

 food as readily as those of the control. 



All animals were bred in pasteboard boxes of identical size at 

 a temperature of from 14 to 19 C. Each chrysalid being kept 

 separately, the duration of the pupal period could be established 



