1 7 2 AN A ceo UNT OF BRITISH FIIES. 



The larvce of Chirononiiis 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 



Fig. 37. — Larva of C. piitmosiis. 



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 larvse 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 algffi {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 Anatoviy. 



Central ?iervoiis 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. 



