AND THE LOWER ANIMALS. 79 



characters of the insect at different periods resemble 

 each other so strongly, that the transformations are 

 almost undistinguishable. We come now to insects 

 with incomplete metamorphoses. 



The Diptera, or true flies, constitute a sort of con- 

 necting link between the above and the groups we 

 have already considered. In these the three stages 

 are very well marked, and certain metamorphoses are 

 rendered more complex by the appearance of a new 

 set of phenomena ; but in the perfect insect we find 

 that the posterior pair of wings is absent, being only 

 represented by a couple of rudimentary organs called 

 balancers, which regulate the flight of the insect. We see 

 then that the Diptera are departures from our ideal plan. 



Let us examine one of these flies, — the chameleon 

 stratiomys (Stratiomys chameleon), which is common 

 enough in the woods about Paris, and whose history 

 has been clearly made out by Reaumur and Swammer- 

 dam. It is a large insect, a little longer and much 

 wider than a bee. From its head spring two fusiform 

 antennae, its two compound eyes are separated by a 

 hairy interval, and its large proboscis, which serves to 

 abstract the saccharine juices from the nectaries of 

 flowers, remains concealed, when at rest, within a 

 special cavity. Its back, which is of a reddish hue, 

 carries, independently of its pair of wings and 

 balancers, two horny curved hooklets, which are 

 directed backwards. Its belly is coloured brown, and 

 is covered with white semilunar spots. Such is the 

 perfect insect. Let us now see what the larva is like. 



This is a sort of flat worm, inflated about the middle, 

 terminating at both ends of its body in a snout-like 

 point ; it is about six or seven centimetres long, com- 



