But a careful examination of the offender, in such instances, will show that it was not a house-fly but probably a stable-fly, which does have mouth-parts fitted for piercing. Three of these veins end rather close together just before the tip of the wing, the posterior one of the group being bent forward rather sharply a short distance from the tip.
Among the so-called haustellate insects the mouth-parts vary so much in different groups, and such different organs separately or combined perform the function of sucking, that the term haustellate loses its significance and even misleads the student. But even in the butterfly, or more especially the moth, there is a good deal of misapprehension about the structure of the so-called "tongue."
There is nothing of the sort here, nothing but absolute inertia, except in the head, where I see, from time to time, the mouth-parts open and close, the palpi give a tremor, the short antennae sway to and fro. A prick with the point of a needle causes no contraction, no matter what the spot pricked. Though I stab it through and through, the creature does not stir, be it ever so little.
The enormous mandibles of the adult Corydalus are too large for use and, as Walsh observed, are converted in the male into simple clasping organs. And to omit a number of instances, in the suctorial Hemiptera or bugs we have different grades of structure in the mouth-parts.
As the sharp cutting organs are thrust deeper and deeper the labium doubles back like a bow and does not enter the skin. Saliva is then poured into the wound through minute grooves in the mandibles, and the blood is sucked up into the mouth by the sucking organ which lies in the head at the base of the mouth-parts.
The superfluous tissue of the gill-structures is used in the improvement of the ear and mouth-parts; a process that had begun in the Amphibian. The body is raised up higher from the ground, on firmer limbs; the ribs and the shoulder and pelvic bones the saddles by which the weight of the body is adjusted between the limbs and the backbone are strengthened and improved.
I trust that the methodical science of the future will take account of these gastronomic laws, to the great relief of the entomological novice, who is too often hampered by the snares of the mouth-parts, the antennae and the nervures of the wings.
Another group containing the Anopheles are intermediate between these two and have mouth-parts fitted for feeding on minute organisms as well as for attacking and holding other larger things. A few kinds feed habitually some distance below the surface, others on the bottom, while still others feed always at the surface.
I find my two larvae turned over, belly downwards; much more: they are half-buried in the mould. When teased, they coil up lazily; they move their legs as well as their mouth-parts, but slowly and without vigour. Then their strength seems to revive. The convalescent, resuscitated grubs dig with clumsy efforts into their bed of mould; they dive into it and disappear to a depth of about two inches.
In the Tardigrades, a long step lower, we have unjointed fleshy legs armed with from two to four claws, but the mouth-parts are essentially mite in character. A decided worm feature is the fact that they are hermaphrodites, each individual having ovaries and spermaries, as is the case with many worms.