of specific size could be associated with any of a complete range of blood hormone con- 

 centrations. 



It is therefore suggested that although corpora allata volumes may be related to 

 activity, size need bear no relation to blood hormone concentration or to the responses 

 induced by corpus allatum activity. 



E. Thomsen (Denmark). 1. A seeming discrepancy in the function of an endocrine 

 organ in different species of insects could be due to a difference in their developiTiental 

 physiology. 



For instance Prof. Johansson's results in Oncopeltus seem to show a difteience 

 in the function of the m. n. с of the adult Oncopeltus as compared with Calliphora. 

 However, the young imago of Oncopeltus contains such a lot of reserve substances brought 

 over from the last larval stage that it is able to live for about 30 days on water alone, 

 and provided with an active с all. such starved insects are even able to produce ripe eggs. 



Not so Calliphora, which will die in about 2 ^/2 — 3 days if only given water; also the 

 implantation of active c. all. into flies fed on sugar and water does not provoke egg de- 

 velopment. 



Thus the abundance of reserve substances in the adult Oncopeltus makes it difficult 

 to decide whether like in Callipliora the m. n. с might have an influence on the building 

 up of substances necessary for egg development. 



2. Experiments in which juvenile hormone (which I got from Dr. Karls on) was 

 injected into allatectomised females of Calliphora gave a negative result as far as egg 

 development Was conc3rned. 



J. de Wilde (Holland). (Antagonistic action between corpora allata and prothoracic 

 glands). Following the model of the action of moulting hormone and juvenile hormone 

 as given by Wiggles worth in the Growth Symposium (Symposium of the S.E.B.,no. 11, 

 1951; pag. 204 — 227), the action of both hoi-mones has been thought to be more or less 

 complementary. The moulting hormone promoting cell division and perhaps protein 

 synthesis, and the juvenile hormone determining the differentiation of cellular characters. 

 Some recent observations seem to be in contradiction to this view. In this respect, I point 

 to a paper by Highnam {Quart. J . Micr. Sei., 99, 1958), in which it is shown that the 

 corpora allata are extreinely active in the beginning of pupal diapause in Mimas tiliae L. 

 Their size diminishes as soon as diapause is being broken. Also in the work of St aal 

 at our laboratory it seems that implantation of corpora allata may cause a delay in moult- 

 ing in the migratory locust {Locusta migratoria L.) These observations suggest that the 

 action of juvenile hormone and moulting hormone may be to some degree antagonistic. 

 St would be interested to hear if our colleagues have evidence in favour of this idea. 



(Role of the prothoracic glands in moulting.) Although the classical conception of the 

 action of the moulting hormone is such, that this hormone would be secreted in regular 

 intervals before each moulting cycle, there is evidence that in many insects moulting 

 still may occur after removal of the brain or prothoracic glands. In this respect, I point 

 to the data of Hachlow with Rhopalocera, andStellwaag-Kittler with Tenebrio molitor 

 L. Last year Mr. Houx at our laboratory found that an isolated abdomen of a prepupal 

 larva of Leptinotarsa could make two successive moults ending in an adult abdomen. 

 One may wonder, if we may suppose that this phenomenon is caused by the remaining 

 titre of the moulting hormone still present (the moulting process itself being self timing). 

 Another possibility might be that the abdomen contains endocrine organs of unknown type. 



(The conception of neuro-hormones.) I think it is very fortunate that we have Profes- 

 sor Gers с h among us, who has recently made such interesting contributions as regards 



218 



