BROOK INSECTS 



67 



gills) project, and wave gently in the water. These 

 cornucopias are the pupae of the black-flies ; that 

 is, the black larvae transform into these cornu- 

 copias, and from the cornucopias finally come the 

 winged black-flies. If there are no pupae among 

 the black-fly larvae when you first find the colony, 

 return occasionally to the spot and you will cer- 

 tainly find pupae in time. 



Fig. 40. A Black-fl/ 



