32 



The Larva of Chironomiis 



The eyes and antennae often disappear altogether in 

 larval Brachycera, while the mouth-parts may be repre- 

 sented, if at all, only by a pair of large hooks (larvae of 

 Muscidae), whose homology with true mouth-parts is not 

 yet adequately established, or by a single crescentic plate 

 armed with saw teeth, which is perhaps the last vestige of 

 the submentum. This extreme ])hase of reduction occurs 

 in the larva of Phytomyza. The fore part of the head 

 consists in this larva of a hammer-shaped chitinous rod, 

 which bears in front the toothed crescentic plate. The 

 rod is articulated behind to a rudimentary skeleton, con- 

 sisting mainly of a pair of apodemes for muscular attach- 

 ment. The hammer-shaped rod is swept to and fro like 

 a scythe, and knocks off the green cells of the leaf, which 

 are passed down the gullet. 



Retraction and reduction of the larval head are usuall}^ 

 associated with retraction of the brain, which often 

 recedes into the prothorax, or, in the case of the blow-fly 

 larva, into the metathorax. 



The ap- 

 pendages 

 of the 

 thorax and 

 abdomen. 



The protlioracic appendages are short, united at the 

 base, and armed with numerous hooks ; 

 they are used in grasping the food, in 

 creeping, and in holding on to the 

 burrow. Shortly before a moult new 

 sets of hooks may be seen within the 

 functional a]3pendages ; these become 

 exposed when the old skin is cast 

 (fig. i). Segments 2-1 1 (not count- 

 ing the head) bear no locomotive aj^pen- 

 dages. The twelfth and last segment 

 bears a pair of long, straight appen- 

 dages, often called the anal feet (figs, i, 

 20) They are armed with a few stout 

 curved spines, which show projecting 

 cusps where they are attached to the 

 chitinous cuticle, resembling in this the setae of some 

 Oligochaet worms, or the hooks on the head of a tape- 

 worm. Before a moult the new coronet of hooks may be 



Fid. 20. — Larva of 

 Chlronomus dorsalis. 

 Anal foot, showing its 

 crown of hooks, the 

 retractor mnscles, and 

 the formation of a new 

 crown of hooks, i^re- 

 paratory to change of 

 skin. (From MiaU's 

 Natural History of 

 Aquatic Insects.) 



