Al'HIDlVOEOUS SYEPIIID.E. 119 



They are of various sizes and colours, and usually are 

 traversed by a white, yellow, or purplish stripe down 

 tlie back, occasioned by the tints of their movable 

 viscera showing through their transparent skins. 

 Some species are provided with two posterior cylin- 

 drical processes, the use of which is not known. 



Between each advancing step the maggot makes a 

 rapid lashing motion of its head in search of its food, 

 and when an Aphis is struck, it is taken off its legs 

 and hoisted into the air, where its juices are rapidly 

 extracted, and then the empty skin is rejected. 



The voracity of the creature has been remarked by 

 Reaumur and Bonnet. The latter says of les Mange- 

 pucerons, " On la voit (la tete) s'allonger et se rac- 

 courcir, s'arrondir et s'applatir, se contourner tantot 

 en un sens et tantot en un autre, et cela avec un 

 promptitude surprenant. Il-y-a aucun animal car- 

 nacier qui chasse avec plus d'avantage " with its 

 trident or dart. 



It is said that the smaller kinds often become the 

 prey of the larvse of the Hemerohiidce or golden-eyes. 



When full fed the larvag attach themselves to leaves 

 or stems, and metamorphose into short, oval pup^e. 

 These hang with their heads downwards, and are 

 covered with a hard and horny skin crossed by nume- 

 rous transverse bars. 



The ova of the Syiyhidce to the naked eye are very 

 like the shining oval bodies glued by the bot-fly to the 

 hairs of the horse's forelegs. They are interesting 

 objects for the microscope, as the chorion or outer 

 shell is studded with elaborate bifurcate papillae. The 

 eggs are singly deposited, and may be often seen on 

 the leaves of the oak, fir, &c., where they are placed 

 in the midst of Aphis food, ready grown for the use of 

 the young grub directly it has hatched out. 



By the law of retahation Pteromalus ovulornm and 

 Chrysolampus tristis oviposit in the eggs of Syrphus, 

 so that these dipterous larvae are often doomed before 

 birth. 



