332 STEFAN KOPEC. 



the cooperation of stimulus of the brain and of the physiological 

 conditions of larval tissues (without which the influence of the 

 brain would have no effect) would appear to be indispensable. 



For these transplantations I used the sexual glands. The gonads 

 of moths do not belong to those organs which develop in the 

 chrysalis from the special imaginal discs ; they are formed by the 

 growth and histological changes of the small larval sexual glands 

 whose existence has been observed for a long time in caterpillars. 

 All four ovarial tubes of caterpillars hitherto contained in a con- 

 nective tissue membrane and forming together with it one appar- 

 ently globular body grow during the caterpillar's pupation to such 

 a degree that they break out of the membrane. In the testes, on 

 the other hand, the characteristic high cylindrical epithelium which 

 lines the interior of that part of the developing spermiduct adjacent 

 to the testicles is formed at that period from the uniform mass of 

 imperfectly separated cells situated at the base of the gland. At 

 the same time the testicle shrinks considerably and its contents 

 become much compacter. I mention these facts in somewhat 

 greater detail than usual in order to emphasize that, although they 

 do not develop from imaginal discs, the sexual glands exhibit cer- 

 tain distinct evolutive changes during their development. As a 

 consequence of this the study of the behavior of the organs after 

 the transplantation is quite suitable for our present purpose. The 

 ovaries and testicles of caterpillars after the third or fourth moult 

 were transferred to full-grown caterpillars which were to undergo 

 pupation in a few days. Hence, in these caterpillars, the substance 

 which excites 'histolytical processes had already passed over from 

 the brain into the body. It was found that the rate of evolution 

 of the testes and the ovaries grafted remained unchanged, notwith- 

 standing the new surroundings in which the processes of meta- 

 morphosis were just beginning or had already begun. From this 

 follows the important conclusion that the stimulus of the brain is 

 inadequate for metamorphosis of the separate organs of insects, 

 and that it is only able to act when the organism, having attained 

 a certain stage of development, is prepared physiologically to re- 

 spond to the stimulus. 



