THE HALTERES OF THE BLOW-FLY. 617 



Eristalis and Calliphora usually fall perpendicularly when 

 thrown into the air, and do not attempt to fly ; that a Calli- 

 phora in which both capitella had been removed could not 

 fly more than two to three metres ; and he states that he has 

 kept Blow-flies alive from thirty-five to forty-four days after the 

 operation. 



Further, he says that the loss of one balancer renders flight 

 difficult. ' The animal flies badly, with uncertainty, unsteadily, 

 and is easily caught.' And he thinks that Eristalis, Musca, 

 and Calliphora are less able to fly when the head of the halter 

 is destroyed than when the whole organ is removed. 



It is most difficult to remove the entire halteres without 

 doing violence to other parts at the same time ; and, bearing 

 in mind the large size of their nerves, it is almost impossible 

 to say how far the thoracic ganglion suffers from their entire 

 ablation, however skilfully performed. 



My own experiments lead me to the following results : It is 

 only possible to remove the whole halter by tearing it away 

 with forceps. When this is done, such serious injuries usually 

 result that the insect becomes perfectly helpless and soon 

 dies. I have already referred to the results of this operation 



(P- 377)- 



Grave injuries to the thoracic ganglion also apparently com- 

 plicate the phenomena observed, and paralysis of the legs, 

 commencing in the hinder pair, usually follows the injury if the 

 animal lives three or four hours. 



Cutting off the head of the halter and part of the stalk can 

 be effected without inflicting other serious injuries, by a skilful 

 operator. When this is done, removal of part of one halter 

 renders flight difficult and clumsy. The insects are easily 

 caught again. Removing the distal part of the second halter 

 gives rise to almost entire loss of the power of flight. Insects 

 so mutilated cannot fly more than a few inches, and when 

 thrown into the air they fall perpendicularly. 



In bright sunlight, however, they will fly clumsily several 

 metres, but they never do so in diffused daylight. This 

 is probably the result of the need of a strong light for 



