INCEPTION OF INSECT METAMORPHOSIS. 333 



C. THE INDEPENDENCE OF THE FURTHER PROCESSES OF 



METAMORPHOSIS. 



I have already mentioned that the brain exerts an influence on 

 the inception of processes of metamorphosis at a certain definite 

 period of the larval life, in females of Lymantria dispar L. of my 

 breed between the seventh and tenth day after their last moult. 

 The question arises as to whether this influence, which excites the 

 inception of histolytical processes in caterpillars, at the same time 

 makes the further course of metamorphosis possible, leading to the 

 formation of the imago ; or whether brainless chrysalids are unable 

 to become moths. When the caterpillar has been influenced by the 

 brain sufficiently to undergo pupation, the further evolutive proc- 

 esses, which take place in chrysalids, have been shown to occur 

 independently of the brain. By comparing the data relative to the 

 length of life of the chrysalids in various specimens (brainless, 

 those used as standard, and normal) we see, moreover, that even 

 the rate of formation of the imago from the chrysalis undergoes 

 neither retardation nor acceleration when the brain is removed 

 (cf. Tables I. and II.). If a caterpillar deprived of its brain 

 undergoes pupation, the emergence of the moth from the chrysalis 

 takes place at the normal time. The removal of the brain or of 

 other ganglia has merely a local effect in that (as I want to point 

 out in another paper) muscles are completely or almost completely 

 absent in the corresponding segments. The absence of muscles, 

 however, is the result of merely local correlation between the pres- 

 ence of the imaginal muscles and that of the nervous ganglion in 

 a segment of the body, but it has no connection with the influence 

 under discussion i.e., the influence of the larval brain on the whole 

 histolytical and evolutive processes during the metamorphosis of 

 insects in all tissues of the whole body. 



The following experiments were made to demonstrate the above 

 principle, viz., that the further metamorphosis of insects, having 

 once been excited by the influence of the brain, continues inde- 

 pendently in a different manner. Evidence ought to be furnished 

 by the metamorphosis of imaginal discs of single parts of the in- 

 sectal body, if it should take place independently of the surround- 

 ings to which they had been artificially transferred. According to 



