BRAIN AND EYES OF LEPIDOPTERA 463 



layer' running abnormally. I was, however, not able to find 

 any nerves radiating from the eye deeper into the interior of the 

 body. 



THE DEVELOPMENT OF THE BRAIN IN INSECTS DEPRIVED OF THE 



GERMS OF EYES 



In the following series of experiments I removed the above- 

 mentioned plate, which contained the material for the eye of the 

 moth, from one side of young caterpillars after the second or 

 third moult, and without depriving the animals of the brain. 

 I examined its behavior in cases when the removed hypodermis 

 did not undergo regeneration and thus did not form an imaginal 

 eye. At the same time the non-operated side of the head could 

 be used as a standard. It was my intention to ascertain whether 

 the morphological and histological metamorphosis which the 

 larval brain undergoes when metamorphosing into the imaginal 

 organ, is in any way dependent on the development or presence 

 of the eye. 



In its principal part the brain of the moth is composed of the 

 large optic gangha resulting from the metamorphosis of those 

 external parts of the larval brain, which form the optic ganglia 

 of the caterpillar (cf. Johansen, '92, and Bauer, '04). In all the 

 specimens which did not regenerate their eyes the imaginal 

 optic gangUon was more voluminous, though shorter on the 

 operated side than on the normal one. The granular, as well as 

 the molecular layer and the ganglion-cell layer (Korner, Moleku- 

 lar and Ganglienzellenscliicht of Berger), was never developed. 

 It follows from the paper of Berger that the tissue which gives 

 rise to these layers is situated in the external parts of the larval 

 brain. This tissue remained intact in the head of the caterpillar 

 operated upon: this I conclude from the fact that I never ob- 

 served any injuries of the larval brain when, to verify the results 

 of operation, I examined the microscopical sections of several 

 specimens directly after operation. In other words, the absence 

 of this layer of the optic ganglion in specimens which had no 

 regenerated eye can only be interpreted by the absence of some 

 developmental stimuh, derived from the normal eye in course of 



