. Text book of zoology. Zoology. Glass 3. Insecta. Order 1. Orthoptera. 255 labial palps, but witii a very broad labium. The legs feeble. Abdomen usually elongate witb two unjointed cerci. Extremely good fliers, seizing their prey {e.g. Butterflies) upon the wing.* The larvEe inhabit fresh water, and are- characterised by the modification of the labium into a long eversible prehensile organ (the mask), and further by the closure of all the stigmata; respii-ation is effected by means of tracheal gills which in some cases are lamellate and situated at the end of the abdomen, whilst in others the

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. Text book of zoology. Zoology. Glass 3. Insecta. Order 1. Orthoptera. 255 labial palps, but witii a very broad labium. The legs feeble. Abdomen usually elongate witb two unjointed cerci. Extremely good fliers, seizing their prey {e.g. Butterflies) upon the wing.* The larvEe inhabit fresh water, and are- characterised by the modification of the labium into a long eversible prehensile organ (the mask), and further by the closure of all the stigmata; respii-ation is effected by means of tracheal gills which in some cases are lamellate and situated at the end of the abdomen, whilst in others they are represented by a number of folds developed in the rectum; in the latter case the rectum receives and ejects water rhythmically. The larvse of the last species move by spirting the water out of the rectum. Here belongs the genus Libellula, in which the hind wings are- broader at the base than at the tip, and the large eyes are pushed together into the middle of the head; the larva) -with rectal branchiae: also the delicate slim .4jrrio)i-species (Demoiselle flies) in which the hind wings are narrower at their- bases than at the ends, the eyes are -wide apart and the larvse possessed of three external gills. 9. May-flies (genus Ephemera and others) are usually small insects with four thin wings, of which the hinder are smaller than the anterior. The- mouth-parts of the imago are rudimentary; the abdomen -with three anal filaments posteriorly. The lai-vae live in water, and like the Dragon-flies possess a closed tracheal system and leaf-hke or branched tracheal gills, situated in a row along each side of the abdomen; they exhibit three thread-like ap- pendages, as does the imago. The larvaa are pre- daceous, and have well-developed mouth-parts ; some of them dig passages in banks. The May-flies pass through a sub-imaginal stage (c/. p. 247); as imagines they take no food, and many species live for only a few hours during the night, metamorphosis occurring in the evening; oth

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