External Parasites 221 



the birds most likely to be infected are those with a deficient 

 supply of oil in the skin. The conditions which favor its 



_ 



■4 ■ V 



Fig. 44. — Photograph of the six-legged larva of Knemidocoptes (Derma- 

 ioryctes) mutatis. (After Haiduk.) 



spread in a flock are dry, barren runs, especially on alkaline 

 soils or in yards filled with ashes or cinders. Foul roosting 

 places also favor the spread of the disease. The disease is 



