DIPTERA. 39 



These four blades or fins have the power of separating from each 

 other. Each segment of the abdomen has on both sides a tuft of 

 hair, and the thorax has three. The head is round and flat, and is 

 provided with two simple brown eyes. Round the mouth are several 

 wattles, furnished with hair, of which two of crescent-like form are 

 the most conspicuous. These tufts move with great quickness, 

 causing small currents of liquid to flow into the mouth, by means of 

 which the necessary food, microscopic insects and particles of vege- 

 table and earthy matter, is brought to the larva. 



They change their skin several times during their continuance in 

 this state. This latter fact has been remarked by Dom Allou, a learned 

 Carthusian, "whose pleasure," says Reaumur, " consisted in admiring 

 the works of the Almighty, when not occupied in singing his praises." 

 We think it will be interesting to repeat the few lines which accom- 

 pany the mention made by Reaumur of this worthy Carthusian. 

 They appear to us to be well worth reading, even at the present day. 



" If the pious monks who composed so many societies, possessed, 

 like Dom Allou, the love of observing insects, we might hope that 

 the most essential facts in the history of those little creatures would 

 soon be made known to us. What enjoyment more worthy of the 

 calling they have chosen could these pious men pursue than that 

 which would place before their eyes the marvellous creations of an 

 Almighty Power ? Even their leisure would then incline ^them, to 

 adore that Power, and would furnish them the means to 

 make others do so who are occupied by too serious or too 

 frivolous employments." 



After having changed its skin three times in a fortnight 

 or three weeks, the larva of the gnat throws off its covering 

 for a fourth time, and is no longer in the larva state. It is 

 changed both in shape and condition. Instead of being 

 oblong, its body is shortened, rounded, and bent in such a 

 way that the tail is applied to the under part of the head. 

 This is the case when the animal is in repose ; but it is 

 able to move and swim, and then, by bending its body and! 

 straightening it again, propels itself through the water. 



In this new condition, that is to say, in the pupa state 

 (Fig. 29), it does not eat. It no longer possesses digestive 

 organs, but it is necessary, even more than before its meta- thena 

 morphosis, that it should breathe atmospheric air. Besides, 

 the organs of respiration are greatly changed. During the time the 

 insect was in the larva state, it was through the long tube fixed to 

 the posterior part that it received or expelled the air ; but in casting 



