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Melinda cognata Meigen 
( a ) Onesia Rob.-Desv. (1830). Characters of the genus and 
LIFE-HISTORY. 
Characters of the Imago. Plump greenish flies; feathering of arista short 
and confined to basal portion, much as in Sarcophaga; cheeks wide; alulae 
covered with dark hairs as in Calliphora; male genitalia large and prominent; 
two post-sutural intraalar bristles; three strong sternopleural bristles; claws 
and pulvilli of male elongated. 
Life-history. 
Geoffrois and Robineau-Desvoidy (1830) were the first to find that these 
Diptera are viviparous. For 0. sepulchralis this was also stated by Schiner 
(1862, p. 576). The latter adds that Onesia larvae‘live upon animal sub¬ 
stances, but his statement is merely based on analogy and not upon actual 
observation. 
During my research on Pollenia rudis F. (1915 a , pp. 91-105) the larvae of 
which live as parasites in the earthworm, I often noticed that the worms 
Allolohophora foetida Eisen., caliginosa Sav. and chlorotica Sav. contained in 
their vesicula seminalis a few first stage Dipterous larvae other than those of 
Pollenia. These larvae were always dead and surrounded by phagocytes. 
Being at first unable to identify them, I called them by a letter A. Subse¬ 
quently, I found that the worms which usually contained these larvae (A) 
showed also third stage larvae occupying in the host the same position as 
those of Pollenia rudis. 
But, unfortunately, when these larvae left the earthworms they were 
infested and killed by a fungus thus making it impossible for me to identify 
them. I called these third stage larvae by the letter B supposing them to 
belong to the same fly as larvae A. 
Finally, on dissecting some Onesia females from the Cambridge Entomo¬ 
logical collection, I found that the flies contained in their uterus nearly 250 
well-formed larvae which proved to be identical with larvae A, thus showing 
that the first stage larvae of Onesia penetrate into the vesicula seminalis of 
different species of common earthworms. 
As to their ultimate development, all I can say at present is that if the 
third stage larvae B belong to the same species of fly as larvae A, the life- 
history of Onesia should be similar to that of P. rudis , i.e. from the vesicula 
seminalis of the earthworm, the first stage Onesia larva migrates to the 
host’s prostomium, this is perforated by the insect’s posterior end so that 
its spiracles communicate with the air. In this position the larva passes 
through two moults or three stages, destroying the earthworm more or less 
completely. 
This is all that we know at present of the life-history of the genus 
Onesia. 
