INCEPTION OF INSECT METAMORPHOSIS. 339 



problem. The whole question demands further research in order 

 to elucidate whether and in what degree there exists an analogy 

 between the physiology of transformation of amphibians and that 

 of insects. 



The following summary contains the more important results of 

 this paper : 



1. The brain (ganglion supra-cesophageale) of the caterpillar of 

 Lymantria dispar L. has particular importance in the general proc- 

 esses of metamorphosis. The presence of the brain is indispensa- 

 ble, at least up to a certain period, for the inception of histolytical 

 processes. The influence of the brain in this direction is probably 

 chemical ; hence the brain ought to be considered as a gland of 

 internal secretion. 



2. At some well-defined time before pupation the quantity of the 

 corresponding substance (or substances) secreted by the brain is 

 already sufficient for the complete pupation of the caterpillar. 



3. Tissues of the caterpillar influenced by the brain undergo fur- 

 ther metamorphosis independently; the germs of the wings of 

 caterpillars grafted shortly before pupation on younger caterpillars 

 near their last moult are transformed in the larval organism into 

 pupal wings in spite of the absence of histolytical processes in the 

 new surroundings. Analogical results have been obtained by trans- 

 plantation of Malpighian tubes and gonads. 



4. It follows from other experiments on the transplantation of 

 organs that the stimulus coming from the brain is not sufficient by 

 itself for the metamorphosis of caterpillars : this stimulus acts only 

 when the insect organism, having attained a certain stage, is physi- 

 ologically prepared to answer to this influence. This is shown by 

 the fact that germs of gonads from young caterpillars grafted into 

 full-grown caterpillars do not undergo metamorphosis character- 

 istic of the pupal development of gonads; in other words, the rate 

 of development underwent no acceleration in spite of the histolyti- 

 cal processes occurring in the new surroundings. 



5. Other parts of the nervous system have no influence on the 

 general processes of metamorphosis. 



6. By making ligatures round the body of the caterpillar and 

 cutting it in different places, we may obtain fragments consisting 

 of front, middle, or hind segments. The front fragments undergo 



