. Handbook of flower pollination : based upon Hermann MuÌller's work 'The fertilisation of flowers by insects' . Fertilization of plants. DIPTERAâHOVER-FLIES 177 to be enclosed in the labial groove. The insect now uses the end-flaps in one of two ways : it either folds them together (as in Fig. 73, i) while the membranous middle piece (y) of the labium is so far retracted that the suctorial apparatus enclosed in the labial groove protrudes in front of the flaps and dips into the fluid to be sucked; or else it spreads out and flattens the flaps so that their rough inner surfaces are closely app

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Image ID: PG28G1
. Handbook of flower pollination : based upon Hermann MuÌller's work 'The fertilisation of flowers by insects' . Fertilization of plants. DIPTERAâHOVER-FLIES 177 to be enclosed in the labial groove. The insect now uses the end-flaps in one of two ways : it either folds them together (as in Fig. 73, i) while the membranous middle piece (y) of the labium is so far retracted that the suctorial apparatus enclosed in the labial groove protrudes in front of the flaps and dips into the fluid to be sucked; or else it spreads out and flattens the flaps so that their rough inner surfaces are closely applied to the flower, and the tip of the suctorial apparatus protrudes from the end of the labial groove. Flies with swollen, cushioned-shaped flaps (Syrphus balteatus, Fig. 75) usually behave in the latter way, those with long, narrow flaps (Rhingia, Fig. 74) invariably adopt the former. Both pollen-grains and fluid which have been carried into the tube formed by the chitinous pieces h and i, are aided in their passage to the mouth by dilatation of the sucking stomach. The laciniae and maxillary palps seem to play no part either in sucking or in feeding on pollen, and hence must be looked upon as useless appendages. 3. In order to bring the proboscis into the sheltered rest position the fly draws the musculo-membranous basal piece (^g) backwards and downwards, the labrum, mandibular piece, maxillae, and maxillary palps fold together above, and the very contractile middle piece (y) is com- pletely retracted, being thrown into a few membranous folds at the lowest part of the proboscis. The chitinous plate («) and the end-flaps (c) simul- taneously fold upwards and forwards, and the complicated proboscis (equally adapted for pollen-eating and nectar- sucking) now lies so deeply hidden â . ⢠^ ât â ⢠, , , ,, «.,â °' ^ â ' Fig. 74. Proboscis of Rhingia rostraia (after Herm. in the deep cavity underneath the Miiller).(l) Head with completely retracted proboscis;

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