. The Cambridge natural history. Zoology. HEAD AND THORAX 99 have then an obscure appearance, and are probably functionally imperfect. In the interior of the head there exists a horny framework called the tentorium, whose chief office apparently is to protect the brain. It is different in kind according to the species. The head shows a remarkable and unique relation to the following segments. It is the rule in Insect structure that the back of a segment overlaps the front part of the one following it; in other words, each segment receives within it the front of the one behind it. Though this i
. The Cambridge natural history. Zoology. HEAD AND THORAX 99 have then an obscure appearance, and are probably functionally imperfect. In the interior of the head there exists a horny framework called the tentorium, whose chief office apparently is to protect the brain. It is different in kind according to the species. The head shows a remarkable and unique relation to the following segments. It is the rule in Insect structure that the back of a segment overlaps the front part of the one following it; in other words, each segment receives within it the front of the one behind it. Though this is one of the most constant features of Insect anatomy, it is departed from in the case of the head, which may be either received into, or overlapped by, the segment following it, but never itself overlaps the latter. There is perhaps but a single Insect {Hypocephalus, an anomalous beetle) in which the relation between the head and thorax can be considered to be at all similar to that which exists between each of the other segments of the body and that follow-. ing it; and even in HypoMplialus it is only -^^ //-^i^ * :/ the posterior angles of the head that over- lap the thorax. Although the head usually ^^^_ head appears to be very closely connected with and front of thorax of ,1,1 1 . ji , T - a beetle, Euchroma: a, the thorax, and is very frequently m re- ^ack of head; b, front pose received to a considerable extent within of pronotum; c, chitin- , â ,,,.. j_i T â ""s retractile band; d, the latter, it nevertheless enjoys great cervical scierites. freedom of motion; this is obtained by means of a large membrane, capable of much corrugation, and in which there are seated some scierites, so arranged as to fold together and occupy little space when the head is retracted, but which help to prop and support it when extended for feeding or other purposes. These pieces are called the cervical scierites or plates. They are very largely developed in Hymenopter
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
