G. S. Graham-Smith 
351 
after these the anterior legs; then the middle and anterior legs; next the 
middle and posterior legs; finally the head and proboscis. Not infrequently 
the wings receive further attention at intervals between the cleansing of the 
various pairs of legs. 
The following procedures are adopted for cleaning the wings. In cleaning 
the upper surface of the wing the posterior leg of the same side is brought 
forward and bent over the proximal part of the wing as it lies horizontally along 
the dorsum of the fly (PI. XVIII, figs. 7, 8), and the leg is then drawn slowly 
backwards along the wing towards its distal extremity. When the leg has 
travelled about half the length of the wing, which in consequence has been 
bent downwards, the opposite posterior leg is brought across under the 
abdomen and placed under the wing so that the tip of the wing is clasped 
between the two legs (PI. XVIII, fig. 9). As the legs pass backwards the tip of 
the wing is drawn between them, and when it escapes from their embrace 
springs back into its usual position (PI. XVIII, fig. 11). 
Sometimes the two posterior legs are used simultaneously for cleaning the 
upper surfaces of both wings (PI. XVIII, figs. 10,12,21,24). Each leg is brought 
forwards and bent over the proximal part of the wing of the same side and 
then drawn very slowly backwards along the wing to its distal extremity. 
The under surfaces of the two wings are generally cleaned simultaneously. 
The wings are raised and the posterior legs are brought forward and bent in 
such a manner that the distal part of the leg passes under the wing with the 
extremity of the tarsus beyond the inner margin of the wing. The wings then 
seem to be pressed upwards till they are almost vertical by the elevation of 
the legs. While in this position they vibrate with such rapidity that it is 
impossible to follow the movements exactly (PI. XVIII, fig. 23). 
During these procedures the fly stands on the anterior and middle pairs of 
legs, the latter pair assuming the position normally occupied by the posterior 
pair. 
When the anterior pair of legs is about to be cleaned the middle pair is 
brought forward in order to obtain a steady position, and the fly sits erect. 
Then the anterior legs are thrust forwards horizontally below the head, which 
seems to be held higher than usual. The cleaning movements are often slow 
and pauses are not infrequent while the legs are applied to each other. Some¬ 
times the tarsi appear to be crossed and rubbed together, but more frequently 
the pulvillus of one leg is applied to the surface of the opposite limb, and drawn 
slowly along it (PI. XVIII, figs. 1, 2, 3, 13). 
When the posterior pair of legs is about to be cleaned the middle pair 
assumes the position usually occupied by the posterior pair, the head is 
depressed between the anterior legs and the abdomen elevated, so that the 
fly appears to be standing on its head. Then the posterior legs are thrust out 
backwards horizontally below the abdomen and rubbed together in the same 
manner as the anterior legs (PI. XVIII, figs. 5, 6, 15, 16). 
The middle legs are cleaned with the aid of the anterior or the posterior 
Parasitology xi 23 
