Studies on the mouth parts and sucking apparatus in the blood-sucking Diptera. No. 1, Philaematomyia insignis, Austen / by F.W. Cragg.

  • Cragg, F. W. (Francis William), 1882-1924.
Date:
1912
Catalogue details

Licence: In copyright

Credit: Studies on the mouth parts and sucking apparatus in the blood-sucking Diptera. No. 1, Philaematomyia insignis, Austen / by F.W. Cragg. Source: Wellcome Collection.

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    •and sending small brandies to them and to the labial salivary gland. In the labella there are only a few very small trachea in the external walls. The Meehan ism of the Pioiioseis. As has already been stated, Philcematomyia possibly feeds both on dung and •on blood, and the structure and mechanism of its proboscis are adapted to both these methods of feeding. So far as the first is concerned, there are no notable •difierences between this fly and the house fly. The proboscis is extended chiefly by the distension of the large air sacs in the rostrum, and by the contraction -of the extensor muscles of the haustellum. The oral lobes are distended by blood, and the fluid sucked up the pseudo-tracheal channels. The mechanism of extension can be readily demonstrated in a freshly-killed insect, in which the proboscis is withdrami, by laymg it on a slide and compressing the front of the head, above the lumde, with a pair of needles. The rostrum at once distends and shoots out from the under surface of the head, and the haustellum straightens itself on the rostrum. The labella are then erected, and can be seen to fill up with a yellowish fluid, which pushes out the pseudo-tracheal membrane of the oral surface, and renders the pseudo-trachea visible. That it is fluid and not air which distends the oral lobes is readily shewn by continuing the pressure : the trachese can then be ruptured, and small bubbles of air collect in the fluid in the labella, floating to whichever surface happens to be uppermost. By further pressure on the rostrum from above downwards one can sometimes rupture the pseudo-tracheal membrane ; the labella then collapse and a small drop of fluid escapes. The labella when extended for use are converted into a bag filled with fluid. The upper portion of the bag, formed by the external walls, is stiffened by the chitinous plates to give a certain amoimt of rigidity to the organ ; the lower part, limited by the flexible pseudo-tracheal membrane, is readily adapted to the surface on which the fly is feedmg, the pseudo-tracheal channels bemg kept intact by the chitmous rmgs, and opened out as the membrane is stretched. The proboscis is withdrawn by the contraction of the retractor muscles in the haustellum, and by the relaxation of the tension in the air sacs. The folding of the labella on the haustellum appears to be brought about by the elasticity of the membraneous walls, which, when the air sacs are no longer distended, and the muscles in the labium relaxed, drives out the blood. Before discussing the mechanism by which the insect obtains blood it is neces- sary to consider the position of the labella, relative to the labium, in the open and
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