324 STEFAN KOPEC. 



natsch ('12, '14) by feeding tadpoles on hypophysis did not bring 

 about it is true any changes in the rate of development, but 

 there is no doubt that feeding experiments with a certain organ 

 may be considered as decisive only if their results are positive, a 

 fact which is not well understood by certain investigators. In fact, 

 Adler ('14), Smith ('16), and Allen ('16, '17) confirm that the 

 processes of metamorphosis in tadpoles are arrested by removal of 

 the hypophysis, which, however, is accompanied by changes in the 

 thyroid. On the other hand, Rogers ('18) and Larson ('19) de- 

 scribed changes of the hypophysis brought about by removal of the 

 thyroid in tadpoles, and Allen ('18) confirmed the fact that tad- 

 poles deprived of their thyroid do not undergo metamorphosis. 

 The question arises, therefore, whether the essential and decisive 

 factor which regulates the transformation in those animals is the 

 function of the hypophysis or of the thyroid. Hirschler ('iS-'ig) 

 ascertained that metamorphosis is accelerated by injecting axolotls 

 with iodoform or iodin. From the recent researches made by 

 Swingle ('ipa and /?), who succeeded in transforming tadpoles 

 deprived of their thyroid by feeding them on iodin with flour, as 

 well as from his own analogous experiments, Allen ('19) draws 

 the general conclusion that the metamorphosis of amphibians de- 

 pends on iodin stored by the thyroid, and that its secretory function 

 is regulated by the hypophysis. 



The relationship of the ganglia of the head to metamorphosis in 

 insects has been studied by Conte and Vaney ('i I ) . These authors 

 made ligatures between the head and the body of caterpillars of 

 Lymantria dispar L. and obtained adult moths. They infer from 

 their experiments that the ganglia of the head are of no importance 

 for these processes. The following pages show, however, that 

 their conclusion is false. We shall see that the brain (ganglion 

 supra-cesophageale) exerts a great influence on metamorphosis of 

 insects, and the cause of the erroneous conclusion will be clearly 

 explained. 



If we wish to investigate the relation which probably exists be- 

 tween the nervous system and the processes of metamorphosis of 

 insects, we must first of all decide whether, after the removal of 

 single parts of the nervous system, the rate of metamorphosis is in 

 general the same as in normal animals, whether it undergoes ac- 



