248 HENRY LAURENS 



larvae and examining the brains it was found that in nearly 

 every case either complete or partial regeneration of the parts 

 concerned had taken place. In some cases only a small epiphysis 

 was present, while in others no difference between this region 

 in the operated larvae and in the normal larvae could be detected. 

 In only 2 larvae sectioned was there no sign of an epiphysis. 

 Therefore another method of getting rid of the epiphysis, etc. had 

 to be resorted to. 



This was to remove it from older larvae after differentiation 

 of the nervous system had taken place. This operation was suc- 

 cessfully carried out on 28 normal larvae ranging in length from 

 12.5 to 40 mm., and in 8 eyeless larvae ranging in length from 12.0 

 to 30.0 mm., from which the optic vesicles had been removed 

 when they were about 5.5 mm. long. In addition to removing 

 the epiphysis the roof of the diencephalon was also cut out in 3 

 normal and 3 eyeless larvae when they were about 12.5 mm. long. 



After the experiments to test the various reactions of these 

 larvae to darkness, light and background had been finished sev- 

 eral of them were killed, sectioned and the brain examined for 

 indications of regeneration of the parts involved. Some of the 

 others were allowed to live until they had metamorphosed, others 

 not quite as long. Eventually the}^ were all of them sectioned 

 and studied. In only one was there any sign of an epiphysis. 



The carrying out of the operation necessary to remove the 

 epiphysis is not a particularly difficult one. The larvae were 

 anaesthetised by placing them in 0.02 per cent chloretone. With 

 a pair of iridectomy scissors a flap of skin was cut and left at- 

 tached at one end so that it could be folded back, after which 

 the roof of the brain case was removed in small pieces until the 

 desired portions of the brain were sufficiently exposed to be 

 removed. Out of a total of 43 operations 28 normal and 8 eye- 

 less larvae survived and grew. 



Again the experiments carried out on larvae operated on in 

 this way showed no differences between those which have al- 

 ready been reported in such detail for normal and eyeless larvae. 

 In addition to simply placing the larvae in darkness and in light 

 on various backgrounds there was carried out a series of experi- 



