432 



INSECTA. 



alternately, and coiling it up about their feet till they arrive at their 

 usual place. 



Of the Maggot. — The maggot is not so long as the caterpillar in pro- 

 portion to its thickness, and is smaller at the two ends than in the 

 middle 1 . Both caterpillars and maggots, as far as I know, have a line 

 of dots on each side, some more, others fewer ; the silk-worm has nine on 

 each side : these are the mouths of the air-canals, which serve as lungs 

 in the caterpillar, as also in the maggot. But, besides this use, in the 

 maggot they serve as air-bladders in those which live in water, and 

 suspend them to the surface of the water, as in the gnat and rat-tail 

 maggot 2 , keeping a globule of air at the tip of the tail, which keeps the 

 maggot near the surface, and water from entering. Some caterpillars 

 have feet for progressive motion, such as those of the butterfly and moth, 

 and these are of two kinds, the six anterior differing in formation from 

 the posterior ones. Some maggots have tails for progressive motion in 

 the water, as those of gnats ; others have them to suspend their bodies 

 by near the surface of the water, as the rat-tail maggot 3 ; while others, 

 which have no progressive motion, as the young ant, and those [larvae] 

 which live in cells, such as of bees, wasps, &c, have neither tails nor 

 feet, although they have progressive motion ; which is by a kind of 

 shortening and elongating alternately their bodies ; and sometimes 

 jumping, as in the maggot of the common nut 4 , and also those in cheese. 



The progressive motion of those that have feet, is a mixture of creeping 

 and walking : the creeping motion is an alternate elongation and con- 

 traction of one half of the length of the body at each time. First, the 

 anterior half lengthens and stretches forward, while the posterior is 

 contracted. The stretched-out head fixes, and this half shortens itself 

 out of the posterior half, which lengthens it ; and, when the posterior 

 half has been pulled out to its full length, then the tail, which was all 

 this time the fixed point, loses its hold, and is drawn forward by the 

 contraction of the posterior half upon itself. The walking is performed 

 at the same time by a successive motion of each pair of feet, which 

 assists in these alternate contractions and elongations of the body, by 

 making a greater number of fixed points, making the head and the tail 

 alternately the fixed point. Those which are aquatic, move their tails 

 like a paddle, as fishes do theirs. 



1 [The experienced entomologist, Mr. Fred. Smith, who has kindly revised the 

 pages relating to Insecta, cites the ' wire-worms,' or larvae of ElateridcB, as exceptions 

 to the above general rule.] 



2 [Musca pendula, Linn.] 3 [lb. Hunt. Prep. Phys. Series, No. 596.] 

 4 [Balaninus Nucum.'] 



