-
Skip These Ads
-
Skip These Ads|
|
 |
Click here and add this page to your favorites!
|
Encyclopedia Britannica - Main :: APO-ARN |
|
|
APTERA (Greek for " wingless ") , a term in zoological classification applied by Linnaeus to various groups of wingless arthropods, including some of the insects, the centipedes, the millipedes, the Arachnida
3. 4. 5. modern zoology the term has become restricted to the lowest order of the class Hexapoda or true insects. This order includes the bristle-tails and the springtails.Many wingless insectssuch as lice, fleas and certain ear-wigs and cockroachesare placed in various orders together with winged insects to which they show evident relationships. In such cases the absence of wings must be regarded as secondary due to a parasitic or other special
several remarkable archaic characters which they exhibit, there is reason for believing that they are primitively winglessthat they represent an early off-shoot which sprang from the ancestral stock of the Hexapoda before organs of flight had been acquired by the class. Characters.In addition to the complete absence of wings and of metamorphosis, the Aptera are characterized by peculiar elongate mandibles (figs. 1, Mn.; 2, 4), with toothed apex and sub-apical grinding surface, like those of certain Crustacea; by the presence between the mandibles and maxillae of a pair of appendages (superlinguae or maxillulae), fig. 1, Mxl., which are absent or vestigial in all other insects; and, in most genera, by the presence in the adult .of abdominalappendagesused for locomotion, these latter varying in number from one to nine pairs. - Among peculiarities of the internal organs the segmental arrangement of the ovaries in most members of the order is noteworthy. Many Aptera are covered with flattened scales like those of moths. Classification.The Aptera are divided into two divergent sub-orders, the Thysanura (q.v.) or bristle-tails, and the Collembola or springtails. Thysanura.The bristle- tails have an abdomen of eleven segments, the tenth usually carrying a pair of long many-jointed tail-feelers (cerci, fig. 1, x.) ; sometimes a median, jointed tail-appendage is also present. To these feelers the popular name is due. There may also be abdominal appendagesin the form of simple unjointed stylets (fig. s, ii.-ix.), accompanied by paired eversible sacs, probably respiratory in functionon eight (or fewer) other abdominal segments. The head of a bristle-tail carries a pair of compound eyes and a pair of elongate many-jointed feelers. The air-tube system is developed in varying degree in different bristle-tails, the number of pairs of spiracles being three (Campodea), nine (Machilis), ten (Lepisma), or eleven (Japyx). Four families of Thysanura are usually recognized. In theMachilidae and Lepismidae (these two families are known as the Ectotrophi) the maxillae are like those of typical biting insects, and there is a median tail-bristle in addition to the paired cerci; while in the Campodeidae and Japygidae (which form the group Entotrophi) the jaws are apparently sunk in the head, through a deep inpushing at the mouth, and there is no median tail-bristle. The cerci in Japyx are not, as usual, jointed feelers, but strong, curved appendages forming a forceps as in earwigs. Collembola.In springtails, or Collembola, the jaws are sunk into the head, as in the entotrophous Thysanura; the head carries a pair of feelers with not more than six (usually four) segments, and there are eight (or fewer) distinct simple eyes on each side of the head (fig. 2, 1, 2). These are in some genera From Carpenter, Proc. R. Dub. Soc. vol. xi. 1. Isotoma hibernica. Side view. 2. ,, Ocelli and post-antennal organ of right side. Tip of terminal antennal segment with antennal organ. Mandible. Tip of left dens with mucro. Outer view 6. 7 like the single elements (ommatidia) of a compound insect eye, in others like simple ocelli. The abdomen consists of six segments only. The first of these usually carries a ventral tube, furnished with paired eversible sacs which assist the insects in walking on smooth surfaces, and perhaps serve also as organs for breathing. From the researches of V. Willem it appears that the viscid fluid which causes the adherence of the ventral tube is secreted by a pair of glands in the head whose ducts open into a superficial groove leading from the second maxillae backward to the tube on the first abdominal segment. The third abdominal segment usually carries a pair of short appendages whose basal segments are fused together; this is the " catch " (fig. 2, 7), whose function is to hold in place the " spring ," which is formed by the fourth pair of abdominal appendagesalso with fused basal segments. In most Collembola the spring appears to belong to the fifth abdominal somite, but Willem, by study of the muscles, has shown that it really belongs to the fourth. The fused basal segments of the appendages form the " manubrium " of the spring, which carries the two " dentes " (usually elongateFrom Knowledge. Mx', Mx2, 1st and 2nd maxillae. ii.-x, Appendages on 2nd to loth ab- dominal segments. The ever- sible sacs on the abdominal segments are shown, some protruded and some retracted. Ovp, Ovipositor. Mn, Mandible, and Mxl. maxillula, dissected out of head. Hind-foot with claws. X 240. Entomobrya anomala. Catch. and flexible), each with a " mucro " at its tip (fig. 2, 5). The fifth abdominal segment is the genital, and the sixth
The spring serves the Collembola which possess it as an efficient leaping-organ (see SPRINGTAIL). But in some genera it is greatly reduced and in many quite vestigial. Most springtails are without air-tubes, and breathe through the general cuticle of the body. But in one family (Sminthuridae) a spirade, opening on either side between the head and the prothorax, leads to a branching system of air-tubes. The Sminthuridae are further characterized by the globular abdomen, which shows but little external trace of segmentation, and by the well-developed spring. In the Entomobryidae the body is elongate and clearly segmented, but the dorsal region (tergum) of the prothorax is much reduced and the head downwardly directed; the spring is well developed. In the Achorutidae the head is forwardly directed, the tergum of the prothorax conspicuous, and the spring small or vestigial. In many genera of springtails a curious post-antennal organ, consisting of sensory structures (often complex in form) surrounded by a firm ring, is to be noticed on the cuticle of the head between the eyes and the feelers. It may be of use as an organ of smell. Other sensory organs occur on the third and fourth antennal segments in the Achorutidae and, Entomobryidae (fig. 2, 3). Distribution and Habits.The Aptera are probably the most widely distributed of all insects. Among the bristle-tails we find the genus Machilis, represented in Europe (including the Faeroe Islands) and in Chile; while Campodea lives high on the mountains and in the deepest caves. The springtails have even a wider distribution. The genus Isotoma, for example, has some of its numerous species in regions so remote as Alaska, Franz Josef Land, the Sandwich Islands, the South Orkneys, Graham Land, Kerguelen and South Victoria Land. As it is unlikely that these delicate insects could be transported across sea-channels, their wide and discontinuous range suggests both their great antiquity and the former existence of continental tracts over which they may have travelled to their present stations. Springtails and bristle-tails live in damp
Geological History.A supposed Thysanuran from the Silurian
Development.The embryonic development of several genera of Aptera, which has been carefully studied, will be more suitably described in comparison with that of other insects than here (see HEXAPODA). BIBLIOGRArny.The modern study of the Aptera may be said to date from the classical memoirs of 1'. Tullbcrg, " Sveriges Podurider," in Kongl. Svensk Vetensk. Akad. Mandl. x., 1872, and Sir J. Lubbock (Lord Avebury), " Monograph of the Collembola and Thysanura," Ray Society, 1873. In these, full references to the older literature will be found. Subsequently our knowledge of the Thysanura has been markedly advanced by J. T. Oudemans, Bijdrage tot de Kennis den Thysanura en Collembola (Amsterdam, 1888); B. Grassi. who published between 1885 and 1889 a series of memoirs entitled " I progenitori dei Miriapodi e degli Insetti," in the Atli Accad. di Scienz. Nat. Catania, and the Memor. R. Accad. dei Lincei; and V. Willem, whose " Recherches sur les Collemboles et les Thysanoures," in Mena. Cour. Acad. Roy. Belgique, lviii., 1900, are indispensable to the student. In addition to this work of Willem, valuable anatomical papers on Collembola have been published by H. J. Hansen (Zool. Anz. xvi., 1893), J. W. Folsom (Bull. Muse Comp. Anat. Harn xxxv
recent
End of Article: APTERA (Greek for " wingless ") If you wish, you can link directly to this article.
<a href="http://jcsm.org/StudyCenter/Encyclopedia/APO_ARN/APTERA_Greek_for_wingless_.html"> APTERA (Greek for " wingless ") </a> |
|
|
(Previous) APT |
(Next) APTERAL (from the Gr. eorrepos, wingless, a-, p... |
Free & Cheap Cell
Phones |
Cheap Long Distance
Phone Service Carriers |
Talk America Local Phone Service
|
Ztel & MCI - Unlimited Long Distance
Compare
Cell Phone Plans & Companies |
International Calling Cards & Prepaid Phone Cards |
Voice Over IP Broadband Internet Phone
Service | Wireless
Phone Plans & Cheap Cell Phones
|
_____________________________________________________________________________
Online First Aid and CPR Certification . The Online Christ Centered Ministries . The Skeptic's Annotated Bible: Corrected and Explained . The Inerrancy Discussion Board . Free Email Accounts . Home Equity Loans . JasonGastrich.com . The Missions, Apologetics, and Creation Bible Conference . Young Earth Creation Science . San Diego Music Lessons . 10,000 Wise Quotes and Spiritual Sayings . Gastrich.net . Maximizing the Internet: 12 Keys to Success . Louisiana Baptist University . NKJV Web Hosting and Services . Michael Newdow . San Diego Soccer Training . Christian Guitar Lessons . Jesus Christ Saves Ministries . Eternal Security
