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VIII. The Development of the Bead of the Imago of Chironomus. By L. C. Miall, 

 F.B.S., F.L.S., Professor of Biology in the Yorkshire College, Leeds, mid A. R. 

 Hammond, F.L.S. 



(Plates XXVIII.-XXXI.) 



Read 17tb December, 1S91. 



Contents. 



Page 



I. Introductio:n — Sketch of the Life-History of Chironomus 2G5 



II. The Imaginal Disks of Weismann 2G6 



III. Description of the Larval Head of Chironomus 2G7 



IV. Description of the Head of the Imago of Chironomus 268 



V. Imaginal Folds in the Head of the Larva of Chironomus 270 



VI. The Process of Pupation in Chironomus 273 



VII. Comparison of Chironomiis with some other Insects 274 



VIII. Conclusion 276 



IX. Explanation of the Plates 277 



I. Introduction. — Sketch of the Life-History of Chironomus. 



It will be desirable to begin by describing very briefly the life-history of Chironomus. 

 The larva abounds in ditches, water-butts, and dirty streams, feeding upon decaying 

 vegetable matter. It makes burrows of particles of earth or leaves, which it weaves 

 together with the very abundant secretion of its salivary glands. The confined situation 

 in which it lives and the scanty supply of oxygen to be found at the bottom of deep 

 pools probably explain the red colour of these larvre, which is due to haemoglobin 

 contained in the blood. The larva often leaves its burrow, and swims through the water 

 with a well-known looping movement. It sometimes rises to the surface, no doubt for 

 respiratory purposes. It is careless about finding its way back to its burrow, and in a 

 short time glues together enough fresh fragments to conceal its body. The red larva, 

 twisting itself into figures of eight, suggested the name of Chironomus, which means 

 harlequin. 



The body of the larva (PI. XXVIII. fig. 1) consists of a head and twelve segments. 

 The prothorax carries a pair of appendages, armed with numerous hooks for grappling, 

 which are particularly useful when the larva advances or retreats within its burrow. A 

 pair of somewhat similar appendages is carried on the last segment of the body, together 

 with two pairs of anal processes. The last segment but one bears two pairs of respiratory 

 tubules. The head, which is small in proportion to the body, bears a pair of short 

 antennae, two pairs of eye-spots, a lal)rum, strong toothed mandibles, a pair of maxilla?, 

 and a labium. The lower exposed surface of the labrum is furnished with a very 

 elaborate set of teeth, hooks, and spines, some of which are probably concerned with 

 guiding the filaments of silk which issue from the salivary glands. 



second series. — ZOOLOGY, VOL. V. 40 



