The house-fly, Musca domestica Linn: its structure, habits, development, relation to disease and control . The metathoracic discs consist of two pairs of smallpyriform masses (fig. 64) h^ing immediately behind the alar discsin the intersegmental line. They are attached to a ventral branchof the lateral tracheal trunk. The anterior rudiment () is thelarger, and forms the imaginal metathoracic leg and sternal region;in the blow-fly and in Volucella it is interesting to note thatthis pair of imaginal discs is situated further forward, and is in 150 THE INTERNAL STRUCTURE OF THE FULL-GROWN LA
The house-fly, Musca domestica Linn: its structure, habits, development, relation to disease and control . The metathoracic discs consist of two pairs of smallpyriform masses (fig. 64) h^ing immediately behind the alar discsin the intersegmental line. They are attached to a ventral branchof the lateral tracheal trunk. The anterior rudiment () is thelarger, and forms the imaginal metathoracic leg and sternal region;in the blow-fly and in Volucella it is interesting to note thatthis pair of imaginal discs is situated further forward, and is in 150 THE INTERNAL STRUCTURE OF THE FULL-GROWN LARVA association witli thf corresponding prothoracic and mesothoracicventral discs. The smaller and more posterior disc () willdevelop into the remaining portion of the much reduced meta-thoracic segment, including the halteres. Reference has already been made to other imaginal rudimentswhich occur in the abdominal region as regular patches of em-bryonic cells. The abdominal segments develop from numeroussegmentally aiTanged plates of a similar nature which are foundduring the early pupal Fig. 68. Transverse section of one of the salivaiy glands of the mature larva. (Cameia lueida drawing.) During pupation the imaginal rudiments increase in size andare not destroyed by the phagocytes in histolysis, as is the caseAvith most of the larval structures. The cephalic discs are evagi-nated by the eversion of their sacs by way of the anterior end ofthe larva, a cord of cells attached to the dorsal wall of the anteriorend of the phar3rnx marking the path of eversion. A similarprocess takes place in the case of the thoracic imaginal discs,which, by their eversion, build up the whole of the skeletal caseof the thorax and its dorsal and ventral appendages, the wings>halteres and legs. PAET III THE NATURAL ENEIVIIES ANL> PARASITES OF THE HOUSE-FLY CHAPTER X ARACHNIDS AND MYRIAPODSClIERXES XODOSUS SCHRANK. There are frequently found attached to the legs of the house-fly sma
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Keywords: ., bookcentury1900, bookdecade1910, bookpublishercambridgeuniversit
