512 Observations on Habits and Parasites of Common Flies 
to be. standing on their heads. Some flies were kept in captivity in 
order to ascertain how long these mites remain attached to them. The 
longest period observed was 192 hours. It is very remarkable that the 
flies seldom seem to make any attempt to remove the mites wherever 
they are situated. 
It may be of interest to note that numerous mites of this species 
were found on specimens of M. stctbvlans caught as early as April 26,1916. 
Fig. 7. Hypopial nymph of Tyroglyphus siro ( x 50) from M. clomestica. 
Fig. 8. Holotaspis sp. ( x 30 and nat. size) from M. domestica. 
Fig. 9. Nymph of a Qamasus allied to G. coleoptratorum ( x 20 and nat. size) from 
C. erythrocephala. 
Several photographs of flies with mites attached in different situations 
are reproduced in Plate XXIX, figs. 1-7. 
The Gamasus was present in great numbers, especially from August to 
October, on the remains of decaying animal matter on which larvae were 
feeding. Moreover they remained plentiful on such material throughout 
the following winter. They are occasionally seen on healthy flies, but 
do not seem to attach themselves permanently like the Holotaspis does, 
