6 2 NORTH AMERICAN DIPTERA. 



the Cecidomyidae is an excellent example of extraordina- 

 ry reduction of wing veins, palpal joints and tarsal joints, 

 though it still retains the primitive antennae and other 

 primitive characters which ally it with the more gener- 

 alized forms of diptera. In other words, the evolution of 

 characters in the different lines of descent does not pro- 

 ceed pari passu, and opinions will always differ as to the 

 different values to be assigned to the specialized char- 

 acters. Nycteribia and Melophagus are perhaps the most 

 highly specialized of all insects, that is they have traveled 

 further from the starting point. We do not for that 

 reason deem them the most typical of insects, the most 

 highly developed far from it. 



COLLECTION AND PRESERVATION 

 OF DIPTERA. 



Flies must be collected with much more care than can 

 be safely used with such insects as coleoptera. Moisture 

 of all kinds injures or ruins them, and specimens collected 

 in alcohol are worthless. For this reason the collecting 

 bottle should be lined throughout with blotting paper, 

 and the cyanide placed in the cork ; a very little poison 

 suffices to kill them. Nor should they be allowed to be- 

 come too dry before pinning. The pin should be thrust 

 through the middle of the thorax, and the specimen 

 placed just so as to enable the head of the pin to be grasp- 

 ed by the thumb and finger safely. Very small speci- 

 mens should never be glued to card points, as is commonly 

 done with coleoptera; they should always be pinned. 

 Sometimes specimens may be collected and packed in 

 some very fine, light sawdust impregnated with carbolic 

 acid, where it is inconvenient or impossible to pin them. 

 Such specimens being gently separated from the sawdust 

 are allowed to remain for some hours, over, but not 

 touching, damp sand before pinning. To pin the small 



