ANIMALS FED UPON 



37 



The question then arises, does this come from birds 

 or reptiles ? In 1911-12 careful measurements were 

 made in forty-six cases, that is, from blood taken from 

 flies that had fed recently enough to allow the corpuscles 

 to be measured unaltered by digestion. 



In each case fifty corpuscles were traced with the camera 

 lucida, and the average measurements obtained for com- 

 parison with known types. Although in some cases a 

 given specimen was with difficulty allotted to any one 

 type, the following result was arrived at : 



In two cases birds appear to have been the source. These 

 would in all probability have been cormorants or darters, 

 which so often sit on a branch at the edge of the water 

 with the wings spread open ; but the herons and ibis which 

 frequent the shore may also be bitten. 



Nearly 57 per cent, of the blood derived from reptiles 

 seems to have come from lizards, probably entirely from 

 the great monitor or Varanus, but measurements of the 

 corpuscles from it and one of the common small brown 

 lizards did not allow any distinction to be drawn. 



There is no possible doubt that Varanus is a most 

 important source of food. I have several times seen one 

 slowly sculling along the surface of the water near the 

 shore, with the top of its head black with Glossina which 

 were evidently so troublesome that at intervals the 

 reptile submerged its head beneath the surface, only 



