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Rh suppression of the conclusion may have the effect of emphasizing the idea which necessarily follows from the premises. Far commoner is the omission of one of the premises which is either too clear to need statement or of a character which makes its omission desirable. A famous instance quoted in the Port Royal Logic, pt. iii. ch. xiv., is Medea’s remark to Jason in Ovid’s Medea, “Servare potui, perdere an possim rogas?” where the major premise “Qui servare, perdere possunt” is understood. This use of the word enthymeme differs from Aristotle’s original application of it to a syllogism based on probabilities or signs ( ), i.e. on propositions which are generally valid ( ) or on particular facts which may be held to justify a general principle or another particular fact (Anal. prior. xxvii. 70 a 10).

See beside text-books on logic, Sir W. Hamilton’s Discussions (1547); Mansel’s ed. of Aldrich, Appendix F; H. W. B. Joseph, ''Introd. to Logic'', chap. xvi.

ENTOMOLOGY (Gr. , insects, and  , a discourse), the science that treats of insects, i.e. of the animals included in the class Hexapoda of the great phylum (or sub-phylum) Arthropoda. The term, however, is somewhat elastic in its current use, and students of centipedes and spiders are often reckoned among the entomologists. As the number of species of insects is believed to exceed that of all other animals taken together, it is no wonder that their study should form a special division of zoology with a distinctive name.

Beetles (Scarabaei) are the subjects of some of the oldest sculptured works of the Egyptians, and references to locusts, bees and ants are familiar to all readers of the Hebrew scriptures. The interest of insects to the eastern races was, however, economic, religious or moral. The science of insects began with Aristotle, who included in a class “Entoma” the true insects, the arachnids and the myriapods, the Crustacea forming another class (“Malacostraca”) of the “Anaema” or “bloodless animals.” For nearly 2000 years the few writers who dealt with zoological subjects followed Aristotle’s leading.

In the history of the science, various lines of progress have to be traced. While some observers have studied in detail the structure and life-history of a few selected types (insect anatomy and development), others have made a more superficial examination of large series of insects to classify them and determine their relationships (systematic entomology), while others again have investigated the habits and life-relations of insects (insect bionomics). During recent years the study of fossil insects (palaeoëntomology) has attracted much attention.

The foundations of modern entomology were laid by a series of wonderful memoirs on anatomy and development published in the 17th and 18th centuries. Of these the most famous are M. Malpighi’s treatise on the silkworm (1669) and J. Swammerdam’s Biblia naturae, issued in 1737, fifty years after its author’s death, and containing observations on the structure and life-history of a series of insect types. Aristotle and Harvey (De generatione animalium, 1651) had considered the insect larva as a prematurely hatched embryo and the pupa as a second egg. Swammerdam, however, showed the presence under the larval cuticle of the pupal structures. His only unfortunate contribution to entomology—indeed to zoology generally—was his theory of pre-formation, which taught the presence within the egg of a perfectly formed but miniature adult. A year before Malpighi’s great work appeared, another Italian naturalist, F. Redi, had disproved by experiment the spontaneous generation of maggots from putrid flesh, and had shown that they can only develop from the eggs of flies.

Meanwhile the English naturalist, John Ray, was studying the classification of animals; he published, in 1705, his Methodus insectorum, in which the nature of the metamorphosis received due weight. Ray’s “Insects” comprised the Arachnids, Crustacea, Myriapoda and Annelida, in addition to the Hexapods. Ray was the first to formulate that definite conception of the species which was adopted by Linnaeus and emphasized by his binominal nomenclature. In 1735 appeared the first edition of the Systema naturae of Linnaeus, in which the “Insecta” form a group equivalent to the Arthropoda of modern zoologists, and are divided into seven orders, whose names—Coleoptera, Diptera, Lepidoptera, &c., founded on the nature of the wings—have become firmly established. The fascinating subjects of insect bionomics and life-history were dealt with in the classical memoirs (1734–1742) of the Frenchman R. A. F. de Réaumur, and (1752–1778) of the Swede C. de Geer. The freshness, the air of leisure, the enthusiasm of discovery that mark the work of these old writers have lessons for the modern professional zoologist, who at times feels burdened with the accumulated knowledge of a century and a half. From the end of the 18th century until the present day, it is only possible to enumerate the outstanding features in the progress of entomology. In the realm of classification, the work of Linnaeus was continued in Denmark by J. C. Fabricius (Systema entomologica, 1775), and extended in France by G. P. B. Lamarck (Animaux sans vertèbres, 1801) and G. Cuvier (Leçons d’anatomie comparée, 1800–1805), and in England by W. E. Leach (Trans. Linn. Soc. xi., 1815). These three authors definitely separated the Arachnida, Crustacea and Myriapoda as classes distinct from the Insecta (see ). The work of J. O. Westwood (Modern Classification of Insects, 1839–1840) connects these older writers with their successors of to-day.

In the anatomical field the work of Malpighi and Swammerdam was at first continued most energetically by French students. P. Lyonnet had published in 1760 his elaborate monograph on the goat-moth caterpillar, and H. E. Strauss-Dürckheim in 1828 issued his great treatise on the cockchafer. But the name of J. C. L. de Savigny, who (Mém. sur les animaux sans vertèbres, 1816) established the homology of the jaws of all insects whether biting or sucking, deserves especial honour. Many anatomical and developmental details were carefully worked out by L. Dufour (in a long series of memoirs from 1811 to 1860) in France, by G. Newport (“Insecta” in Encyc. Anat. and Physiol., 1839) in England, and by H. Burmeister (Handbuch der Entomologie, 1832) in Germany. Through the 19th century, as knowledge increased, the work of investigation became necessarily more and more specialized. Anatomists like F. Leydig, F. Müller, B. T. Lowne and V. Graber turned their attention to the detailed investigation of some one species or to special points in the structure of some particular organs, using for the elucidation of their subject the ever-improving microscopical methods of research.

Societies for the discussion and publication of papers on entomology were naturally established as the number of students increased. The Société Entomologique de France was founded in 1832, the Entomological Society of London in 1834. Few branches of zoology have been more valuable as a meeting-ground for professional and amateur naturalists than entomology, and not seldom has the amateur—as in the case of Westwood—developed into a professor. During the pre-Linnaean period, the beauty of insects—especially the Lepidoptera—had attracted a number of collectors; and these “Aurelians”—regarded as harmless lunatics by most of their friends—were the forerunners of the systematic students of later times. While the insect fauna of European countries was investigated by local naturalists, the spread of geographical exploration brought ever-increasing stores of exotic material to the great museums, and specialization—either in the fauna of a small district or in the world-wide study of an order or a group of families—became constantly more marked in systematic work. As examples may be instanced the studies of A. H. Haliday and H. Loew on the European Diptera, of John Curtis on British insects, of H. T. Stainton and O. Staudinger on the European Lepidoptera, of R. M‘Lachlan on the European and of H. A. Hagen on the North American Neuroptera, of D. Sharp on the Dyticidae and other families of Coleoptera of the whole world.

The embryology of insects is entirely a study of the last century. C. Bonnet indeed observed in 1745 the virgin-reproduction of Aphids, but it was not until 1842 that R. A. von Kölliker described the formation of the blastoderm in the egg of the midge Chironomus. Later A. Weismann (1863–1864)