Page:1902 Encyclopædia Britannica - Volume 25 - A-AUS.pdf/745

 ARTA — ARTHROPODA and enable him to acquire the power to express himself through different media without forgetting the grammar and alphabet of design. Practice may vary, but principles remain, and there is a certain logic in art, as well as in reasoning. All art is conditioned in the mode of its expression by its material, and even the most individual kind of art has a convention of its own by the very necessities and means of its existence. Methods of expression, conventions alter as each artist, each age seeks some new interpretation of nature and the imagination—the well-springs of artistic life, and from these reviving streams continually flow new harmonies,

689

new inventions, and recombinations, taking form and colour according to the temperaments which give them birth. (w. Cu.J Art a, a town of Thessaly, in Greece, in the province of Arta, 59 miles N.hT.W. of Mesolonghi, on the river Arta, which enters the Gulf of Arta some distance south of the town. The battle of Actium was fought near the mouth of the gulf in 29 b.c. The population is now about 7000.

ARTHROPODA. division or branch, which he called Articulata, including the Arthropoda and the Chaetopoda (Annelides of Lamarck, a name adopted by Cuvier), and differing from it only by the inclusion of the Rotifera. The name Articulata, introduced by Cuvier, has not been retained by subsequent writers. The same, or nearly the same, assemblage of animals has been called Entomozoaria by De Blainville (1822), Arthrozoa by Burmeister (1843), Entomozoa or Annellata by Milne-Edwards (1855), and Annulosa by M'Leay (1819), who was followed by Huxley (1856). The character pointed to by all these terms is that of a ring-like segmentation of the body. This, however, is not the character to which we now ascribe the chief weight as evidence of the genetic affinity and monophyletic (uniancestral) origin of the Chaetopods, Rotifers, and Arthropods. It is the existence in each ring of the body of a pair of hollow lateral appendages, or parapodia, moved by intrinsic muscles and penetrated by blood-spaces, which is the leading fact indicating the affinities of these great sub-phyla, and uniting them as blood-relations. The parapodia (Fig. 7) of the marine branchiate worms are the same things genetically as the “ legs ” of Crustacea and Insects (Figs. 9 and 10). Hence the term Appenmculata was introduced by Lankester (preface to the English edition of Gegenbaur’s Comparative Anatomy, 1878) to indicate the group. The relationships of the Arthropoda thus stated are shown in the subjoined table:— 1 {Sub-phylum 1. Rotifera. As a matter of fact the group Arthropoda itself, thus constituted, „ 2. Chsetopoda. was precisely identical in its area with the class Insecta of Linnaeus, ,, 3. Arthropoda. the Entoma of Aristotle. But by causes which it is not easy to trace the word “Insect” had become limited since the days of Linnaeus The Rotifera are characterized by the retention of what to the Hexapod Pterygote forms to the exclusion of his Aptera. Lamarck’s penetrating genius is chiefly responsible for the shrinkage appears in Molluscs and Chaetopods as an embryonic of the word Insecta, since it was he who, forty years after Linnaeus’s organ, the velum or ciliated praeoral girdle, as a locodeath, set up and named the two great classes Crustacea and Arachnida motor and food-seizing apparatus, and by the reduc(included by Linnaeus under Insecta as the order “Aptera”), assigning to them equal rank with the remaining Insecta of Linnaeus, for tion of the muscular parapodia to a rudimentary or which he proposed the very appropriate class-name “Hexapoda.” non-existent condition in all present surviving forms Lamarck, however, appears not to'have insisted on this name Hexa- except Pedalion. In many important respects they are poda, and so the class of Pterygote Hexapods came to retain the degenerate — reduced both in size and elaboration of group-name Insecta, which is, historically or etymologically, no more appropriate to them than it is to the classes Crustacea and Arachnida. structure. The Chaitopoda are characterized by the possession of The tendency to retain the original name of an old and comprehensive group for one of the fragments into which such group becomes divided horny epidermic chsetse embedded in the integument and by the advance of knowledge—instead of keeping the name for its moved by muscles. Probably the chaetas preceded the logical use as a comprehensive term, including the new divisions, each duly provided with a new name—is most curiously illustrated in the development of parapodia, and by their concentration history of the word Physiology. Cicero says, ‘ ‘ Physiologia naturos and that of the muscular bundles connected with them at ratio,” and such was the meaning of the name Physiologus, given to the sides of each segment, led directly to the evolution a cyclopaedia of what was known and imagined about earth, sea, sky, of the parapodia. The parapodia of Chaetopoda are birds, beasts, and fishes, which for a thousand years was the authoritative source of information on these matters, and was translated into never coated with dense chitin, and are, therefore, every European tongue. With the revival of learning, however, first never converted into jaws; the primitive “ head-lobe ” one and then another special study became recognized—anatomy, or prostomium persists, and frequently carries eyes and botany, zoology, mineralogy, until at last the great comprehensive sensory tentacles. Further, in all members of the term Physiology was bereft of all its once-included subject-matter, excepting the study of vital processes pursued by the more learned sub-phylum Chaetopoda the relative position of the members of the medical profession. Professional tradition and an prostomium, mouth, and peristomium or first ring of the astute perception on their part of the omniscience suggested by the body, retains its primitive character. We do not find in terms, have left the medical men in English-speaking lands in undis- Chaetopoda that parapodia, belonging to primitively postturbed but illogical possession of the words physiology, physic, and oral rings or body-segments (called “ somites,” as proposed physician.

ARTHROPODA is the name of one of the three subphyla into which one of the great phyla (or primary branches) of coelomoccelous animals—the Appendictjlata —is divided ; the other two being respectively the Cheetopoda and the Rotifera. The word “ Arthropoda ” was first used in classification by Siebold and Stannius (Lehrbuch der vergleich Anatoviie, Berlin, 1845) as that of a primary division of animals, the others recognized in that treatise being Protozoa, Zoophyta, Vermes, Mollusca, andYertebrata. The names Condylopoda and Gnathopoda have been subsequently proposed for the same group. The word refers to the jointing of the chitinized exo-skeleton of the limbs or lateral appendages of the animals included, which are, roughly speaking, the Crustacea, Arachnida, Hexapoda (so-called “true insects”), Centipedes, and Millipedes. This primary group was set up to indicate the residuum of Cuvier’s Articulata when his class Annelides (the modern Chaetopoda) was removed from that “ embranchement.” At the same time Siebold and Stannius renovated the group Vermes of Linnaeus, and placed in it the Chaetopods and the parasitic worms of Cuvier, besides the Rotifers and Turbellarian worms.1 The result of the knowledge gained in the last quarter of the 19th century has been to discredit altogether the group Vermes, thus set up and so largely accepted by German writers even at the present day. We have, in fact, returned very nearly to Cuvier’s conception of a great