United States or Montserrat ? Vote for the TOP Country of the Week !
The tip of the abdomen is furnished with a pair of movable organs, which in the male are variously modified and serve as clasping organs at mating time. The mouth-parts of the mosquito have just been described. It will be remembered that the labrum is provided with a groove. Just back of the pharynx is the esophagus which leads to the beginning of the stomach.
There may be some truth in this, but for most of us a bite means a hurt anyway and few will be content to sit perfectly still and watch the little pest gradually fill up on blood. It is not known just what the action of the saliva is, its composition or reaction on the tissues. It is generally supposed to prevent coagulation of the blood that is to be drawn through the narrow tube of the labrum.
During the Mysis-period, the auditory organs in the basal joint of the anterior antennae are formed; the inner branches of the first three pairs of feet are developed into chelae and the two hinder pairs into ambulatory feet; palpi sprout from the mandibles, branchiae on the thorax, and natatory feet on the abdomen. The spine on the labrum becomes reduced in size.
The labrum or upper lip, and the clypeus are large and as distinct as in the embryos of other insects, a fact to which we shall allude again. The large three-jointed spring is now well developed, and the inference is drawn that it represents a pair of true abdominal legs. The embryo when about to hatch throws off the egg-shell and amnion in a few seconds.
The labrum and the complicated lamina formed by the lip and the jaws leave between them a narrow slit in which the mandibles work. The legs are merely vestiges, for, though they consist of three tiny cylindrical joints, they are barely a fiftieth of an inch in length. The creature is unable to make use of them, not only in the liquid honey upon which it lives, but even on a solid surface.
As soon as the wound is made the insect pours out through the tube of the hypopharynx some of the secretion from the salivary glands and then begins to suck up the blood through the hollow labrum into the pharynx and on into the stomach. The mouth-parts of the male differ in some important respects from those of the female.
But what is most remarkable is, that they now appear under two different forms. The terminal setae of the second pair of antennae project between the cheliferous feet. Buccal region of the same from below; lambda, labrum. Head of the rarer form of the male, magnified 25 times. In the first place, and before inquiring into its significance, I will say a word upon this fact itself.
These are the mesothorax and the first eight abdominal segments. As in the Sitaris-larvæ, the last pair of stigmata, that of the eighth segment of the abdomen, is less developed than the rest. The head is horny, of a light brown colour. The epistoma is edged with brown. The labrum is prominent, white and trapezoidal.
So in a less degree does the head of the larvæ of certain Neuroptera and Coleoptera. The eyes are compound, the single facets forming a sort of heap. The clypeus and labrum, or upper lip, is, in all the Thysanura, carried far down on the under side of the head, the clypeus being almost obsolete in the Poduridæ, this being one of the most essential characters of that family.
The labrum is prominent, is not distinctly divided from the head, is curved in front and edged with pale and very fine bristles. The mandibles are small, reddish toward the tips, blunt and hollowed out spoonwise on the inner side. Below the mandibles is a fleshy part crowned with two very tiny nipples. This is the lower lip with its two palpi.
Word Of The Day