On the corpora allata of dipterous insects

It is well known from Nabert’s extensive work (1913) on the corpora allata of the Insecta that these small organs are of general occurrence in that class of animals. In so far as the Diptera are concerned, this investigator gave little attention to that order, and only described the corpora allata in the adults of two species ofTipula . These organs have not so far been described in any of the Diptera Cyclorrhapha. The corpora allata are attracting a good deal of attention at the present time because they are evidently the seat of hormone secretion. Thus, Wigglesworth (1934 and 1936) has shown on good evidence that, in the reduviid bugRhodnius prolixus , they secrete the hormones which are intimately concerned with the processes of ecdysis and metamorphosis. Fraenkel (1935) also has demonstrated that a hormone induces pupation in the blow flyCalliphora erythrocephala. He gave evidence suggesting that this hormone is secreted in the region of the central nerve gangliaand is discharged into the blood. At the same time he did not locate the actual source of the hormone and remarked that “there exists no organ in the fly larva which can be homologized with the corpora allata of other insects”. In the present paper endeavour is made to show that the homologues of these organs are present in the larva ofCalliphora and that there is reason to regard them as the source of the hormone referred to Fraenkel.