concerning tissues react to a lower C. A. hormone level in the absence of the 

 gregarioiis stimulus. 



Which of these possibilities holds good presumably can be solved by the use 

 of rather pure С A. hormone extracts injected in allatectomized 1агл ae sub- 

 sequently^ reared under different conditions. A reliable technique for allatectomy 

 in locust larvae, necessary for testing the implanted corpora allata and extracts, 

 was not available. Pre\ious trials did not succeed very well (Joly, 1949), 

 probably because the damage in the hard cuticle of the head capsule is mostly 

 lethal in moulting. 



Methods 



1. Allatectomy. A new technique was developed in which only the soft 

 neck membrane is severed as this does not disturb moulting apparently. 

 The larvae are fixed in a specially designed apparatus and immersed in saline 

 under a binocular dissection microscope with foot-focussing. Continuous 

 rinsing of the wound with sterile saline through a hypodermic needle permits 

 a very good view into the head cavity. In using this method post operative 

 mortality is not higher than 10 — 20%, and further moulting is not disturbed. 



2. Implantations of C. A. can be carried out with the same apparatus. 

 In our experiments С A. were always fixed to the inner side of the mandibular 

 muscles. This has the advantage that the implanted C. A. can be found again 

 at the end of development and moreover that a good contact of the С A. with 

 freely circulating haemolymph is maintained. 



3. Injection of juvenile hormone-extracts of cecropia in pure or emulgated 

 state were carried out by means of an Agla micrometer syringe. 



Results 



1. Allatectomy in early II stage larvae resulted in a somewhat delayed 

 next moult (up to 1 — 4 days later) during which always more or less adult 

 characters appeared (in pigmentation, cuticle, hairs, wing hypertrophy). Most 

 of these prothetelic IlIrd larvae tried to moult again wdthout much success 

 because of the thick adult cuticle. Some larvae did not moult again and showed 

 the normal colour change of maturing adults, i. e. a change to a dull brown 

 colour accompanied by the simultaneous disappearance of the black mélanine 

 patterns. 



In normal gregarious male adults a yellow maturation colour always appears. 

 This did not occur in these prothetelic larvae, probably while this colour 

 is related to the presence of the C. A. 



To test this possibility, adult С A. луеге reimplanted in a number of recently 

 moulted prothetelic Ilird larvae. This resulted in the appearance of the yellow 

 colour in all surviving larvae starting 5—0 days after the implantation. 



143 



