OCR Text |
Show 4 Cl-tUSTACEA, A HACII~lDES, INSECT A. cover them before and behind are named labia(l ), and the f1·ont one, in particular, labrum. The palpi are articulated filament. attached to the jaws or to the lower lip, and appear to be employed by the animal in recognizing its food. The form of these various organs determines the nature of the regimen with as much precision as the teeth of quadrupeds. The ligula, or tongue, commonly adheres to the lower lip(2). Sometimes, in the Apes and other Hymenopterous insects, it is considerably elongated, as are also the jaws, forming a sort of false proboscis (prom us cis) at the base of which is the pharynx, and frequently covered by a sort of sub-labrum, styled by M. Savigny the epipharynx(3). At other times, (1) We here more particularly allude to Insects with six feet, or to the llexa· pod a. (2) Or rather labium, since the other is termed labrum. It is protected, before, by a horny production formed by a cutaneous pt·olongation, and articulated at the base with an inferior portion of the head called the mentttm or chin. Its palpi, always two in number, are distinguished from those of the maxillc:e by the epithet labial. When the latter amount to four they are designated as external and internal, · they are considered as a modification of the external and terminal division of the maxilla:. This production, which, in his Ulonates or the Orthoptera, Fabricius termed the Galea, is still the same maxillary division, but more dilated, arched, and fitted to cover the internal division which, here, on account of its scaly consistence and of its teeth, resembles a mandible. ln the last insects, a'nd particubrly in the Libellub:, the interior of the buccal cavity presents a soft or vesicular body, dis· tinct from the lip, and which, compared to the Crustacea, appears to be the true tongue-labium, Fab. This part is perhaps represented by those lateral divisions of the ligula termed paraglossa:. (See the Coleoptera Carnivora, Hydrophili, Staphylini, the two pencil-shaped pieces that terminate the lip of the Lucani, Apiarire, &c.) The above mentioned Insects, the Orthoptem and the Libellula:: of Linna::ns, evidently demonstrate that this membranous and terminal portion of the inferior lip, which projects more or less between its pal pi, and is particularly elongated in several of the Hymenoptera, is very distinct from that intemal caruncle which I consider the tongue properly so called; notwithstanding this, nearly all Entomologists designate this external extremity of the lip by the name of ligula, or langttetfe. To say, however, that the tongue properly so called, is usually so intimately connected with the lip that at the first glance they seem to be con· founded, is correct. The pharynx is situated in the middle of the anterior face of this lip a little above its root, and in the Coleoptera provided with paraglossa::, at thei1· point of union. In order to understand well the primitive composition of the under lip, it must be studied in the larva:, and chiefly in those of the Aquatic Carnivorous Coleoptera. See General Observations on Insects. (3) There is a membranous production beneath the labrum, i'n many Coleop· CRUSTACEA, ARACHNIDES, INSECTA. 5 in the Hemiptera and Diptera, the mandibles and maxillre are . replaced by scaly pieces in the form of setre, which are received in an elongated tubular sheath, that is either cylindrical and articulated, or formed with more or less of an elbow, and terminated by a kind of lips. In this case they constitute a tl'ue proboscis. In others that also live by suction, the Lepidoptera, the maxi11re alone are greatly elongated and united, producing a tubular setiform body, resembling a long, slender, and spiral tongue (or the spiritrompe, Lat.); the remaining parts of the mouth are considerably reduced. Sometimes again, as in many of the Crustacea, the anterior feet approach the maxillm, assume their form, and exercise part of their functions-the latter are then said to be multiplied. It may even happen that the true maxillre become so much reduced, that the maxillary feet supply their place in toto. Whatever be the modifications of these parts, however, they can always be recognized and referred to a general type(!). tera, which appears to me to be analogous to the epipharynx. The hbrum is to it, what the mentum is to the labium. (1) It is only by a comparative and gradual study of the mouth of the Crustacea, that we can acquire correct :mel exact ideas respecting the various transformations of these parts, and the means of establishing, if not a certain, at least a probable general concot·dance between these various organs in the three classes. The mandibles, maxillre, and the labium, are in fact, a sort offeet appropriated to the masticatory or buccal functions, but susceptible of being so modified as to become organs of locomotion. This principle even extends to the antenna:, or at least to the two intermediate ones of the Crustacea. By adopting it, we are enabled to reduce the composition of these organs to one general type, and we shall het·eafter see that, in this respect, neither the Arachnides nor Myriapoda. present any anomaly. |