172 AN ACCOUNT OF BRITISH FLIES. 
The larve of Chironomus plumosus. 
The body of the “blood worm” is composed of thirteen segments, 
it is cylindrical in shape, generally smaller at the posterior end. The 
head has four eyes upon it, two on each side, and a few hairs, and 
is armed with a pair of biting mandibles. A spinning organ is also 
present. The second segment is furnished on the ventral surface 
Fic. 37.—Larva of C. plitemosus. 
with a pair of prolegs, the extremities of which are furnished with a 
number of closely set hairs, the third to tenth segments are devoid of 
all appendages. The eleventh and twelfth have each a pair of 
jointed worm-like processes. Each pair is attached to the anterior 
end of its segment, and wave about when the creature is swimming. 
The last or anal segment has a well-developed pair of prolegs which 
terminate in a number of claw-like portions. At the posterior 
extremity of the anal segment are four saccular appendages, and 
above these a dense tuft of hairs. Burmeister considered the prolegs 
branchial appendages ; they are not so, however, but are used for the 
same purpose as the prolegs of the caterpillar are used for. The true 
branchial appendages are the four egg-shaped processes on the anal 
segment. The larve grow rapidly but live some time; they form 
tubes or “‘ houses” at the bottom of the water in which they pass part 
of their existence. These tubes, which are tortuous, are formed out 
of algze (Spirogyra, etc.), bound together with silk from the spinning 
organ of the larva. They leave these burrows, according to Grumm, 
in the species he observed, at night ; such, however, is not the case 
with the blood worm, for they can be seen swimming about at any 
time with their curious wriggling motion. 
Internal Anatomy. 
Central nervous system.—This is made up of eleven ganglia united 
by double commissures in the middle region of the body; some of 
the anterior and posterior ones lie close together. 
