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The structure of the head shows that its generic distinctness from Saperda is well founded, as the head is smaller and flatter, the clypeus being twice as large, and the labrum broad and short, while in S. vestita it is longer than broad. The mandibles are much longer and slenderer, and the antennæ are much smaller than in S. vestita. The beetles, according to Dr. Paul Swift, as quoted by Dr.
The antennæ are inserted high up on the head, next the ocelli, falling down over the clypeal region. The clypeus, however, is merged with the epicranium, and the usual suture between them does not appear distinctly in after life, though its place is seen in figure 167 to be indicated by a slight indentation.
The base of the large, tubular labium, or beak, which ensheathes the mandibles and maxillæ, is opposite the end of the clypeus or front edge of the upper side of the head, and at a distance beyond the mouth equal to the breadth of the labium itself.
This light-armed people, relying more on their activity than on their strength, cannot struggle for the field of battle, enter into close engagement, or endure long and severe actions, such as the poet describes: "Jam clypeo clypeus, umbone repellitur umbo, Ense minax ensis, pede pes, et cuspide cuspis."
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.
A most remarkable distinction between the sexes of many beetles is presented by the great horns which rise from the head, thorax, and clypeus of the males; and in some few cases from the under surface of the body.
The labrum is distinctly defined by a well marked suture, and forms a squarish, knob-like protuberance, and in size is quite large compared to the clypeus.
On observing the living Podura, the mouth seems a simple ring, with a minute labrum and groups of hairs and spinules, which the observer, partly by guess-work, can identify as jaws and maxillæ, and labium. But in studying the parts rendered transparent, we can identify the different appendages. The labrum, or upper lip, is separated by a deep suture from the clypeus, and is trapezoidal in form.
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.
It differs from the G. hologaster of Europe, which lives on the same bird, in the short second joint of the antennæ, which are also stouter; and in the long head, the clypeus being much longer and more acutely rounded; while the head is less hollowed out at the insertion of the antennæ.
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