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 
(Pp. 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 
