176 ANIMAL PARASITES AND MESSMATES. 



Travellers since Azara's. time assure us that Uruguay 

 contains but few oxen and horses, because a fly exists 

 in that country which lays its eggs in the navel of these 

 animals at the moment of their birth. These animals, 

 on the contrary, are abundant in Paraguay. In order to 

 increase their number in Uruguay, it would be necessary 

 to favour the multiplication of birds or insects which 

 make war on these flies, either in the larval or the sexual 

 state. 



Diptera, known by the name of Conops, pass their 

 first three changes in the soft parts of drone-bees. Du- 

 meril had formerly suspected, from the curvature of the 

 abdomen, that the Conops lays its eggs in the body of 

 some other insect. Lachat and Victor Audouin have 

 given an instance of this in the " Journal de Physique." 



Thus the Conops, in its larval state, inhabits the 

 abdomen of drones or other hymenoptera ; the Echino- 

 myse are developed within various lepidoptera when in 

 the state of caterpillars or chrysalids ; there are even 

 some which live on flesh, and prefer that which is in a 

 state of incipient putrefaction. 



We may also speak, in this category, of animals 

 which seek assistance, while young, from neighbours of 

 whom they take advantage during their life, and utilize 

 them even after their death; these are insects of various 

 orders. They are in general more cruel than beasts of 

 prey, which often contend on equal terms with their 

 victims. Here we have an enemy which furtively intro- 

 duces itself into its neighbour, who is nearly sucked dry 

 before he suspects the danger to which he is exposed. 

 He harbours unawares the assassin who is about to 

 murder him. This is the refinement of cruelty. 



