412 MEDICAL ENTOMOLOGY 



its movements are then to a certain extent impeded. It is always 

 advisable to catch a large number of each species when one has the 

 opportunity, in order to be able to study individual variations if this 

 subsequently proves to be necessary, and to have a surplus for exchange. 

 Duplicates are always welcomed at the various Schools of Tropical 

 Medicine and at many Museums. Particular care should be taken to 

 note the flies which feed on the different hosts, even if they are not to be 

 collected. The determination of the common host or hosts of blood- 

 sucking flies, the sites at which they usually bite, and the circumstances 

 under which they will feed on other animals, have been much neglected. 

 All that is required in the way of apparatus is a small net, some 

 collecting tubes, a killing bottle, some pins, a pair of stout bent forceps 

 and a small collecting box. If one is working within 



Apparatus for re ^ c h Q{ a laboratory a net and some test tubes will 

 collecting Diptera. . J . . 



The Net suffice. A simple form 01 net made in the following 



. way is recommended : A stout piece of wire tele- 

 graph wire does very well about two feet long is bent into a circle 

 about six inches in diameter, or considerably smaller for delicate flies, 

 the remainder of the wire being turned into a handle by twisting the 

 two ends around one another. On to this ring is stitched a muslin 

 bag one and a half to two feet long, care being taken to see that the 

 seams are on the outside, otherwise small flies will get caught in them. 

 One should have spare bags in case the one in use becomes dirty or 

 torn ; it is only the work of a few minutes to stitch on a new one. If a 

 longer net is required in order to catch flies resting out of reach, the 

 handle can be tied to a stick. The elaborate and expensive folding nets 

 sold by dealers in entomological outfits are not much use, as they are 

 both too big and too heavy for catching active Diptera ; they very 

 quickly get out of order. 



When the specimen has been netted, it should be driven to the bottom 

 of the bag by a sharp turn of the handle, and then, if it is very active, it 



may be isolated in a part of the net with one hand ; 



Collecting tubes . r 



with the other a tube is passed in and the mouth placed 

 over the fly. Less powerful flies can be readily transferred to a tube by- 

 inverting the mouth over them. The flies may either be collected in small 

 tubes and killed in the laboratory, or they may be killed at once in the 

 killing bottle. For collecting tubes, the most useful are small specimen 

 tubes, 1 x 3 in. or a little larger. The mouth should be closed by 

 a plug of cotton wool, never by a cork ; neglect of this point will result 

 in the early death and probable moistening of the specimens, especially 



