382 IDIOPHYSICS. 



bratula and orbicula ; and the sixth class of mollusca, Cirrhopoda, 

 having tufted filaments instead of feet, includes the lepas or anatifa, 

 and the balanus or barnacle. The shells of these animals are dis- 

 tinguished as univalves, bivalves, or multivalves; according as they 

 consist of one, two, or more pieces. 



7. We would apply the name of Arthrology to the study of 

 Cuvier's third grand division of animals; the articulata ; or worms, 

 crabs, spiders, and insects, having jointed trunks, and mostly jointed 

 limbs. The study of worms, has received the name of Helmintho- 

 logy ; and that of insects, is popularly termed Entomology. The 

 nervous system of the articulata, consists of two long cords, dilated 

 at intervals into knots, called ganglia ; and their covering is composed 

 of rings, either hard or soft ; but they have in other respects wide 

 differences, by which they are subdivided into classes. The first 

 class, Jlnnulata, including red blooded worms, is the only class of 

 the articulata which has red blood : and it comprises the Tubicolae, 

 as the serpula, sabella, and terebella, which have shells ; the Dorsi- 

 branchiata, having branchiae or gills along the back, as the sand 

 worm, eunice, and nereis; and the Abranchiata, which respire only 

 through the skin, as the earth or angle worm, and the leech or blood- 

 sucker. 



The remaining articulata, called by Linnaeus insecta, are dis- 

 tinguished by having at least six articulated, that is jointed feet. 

 The second class, Crustacea, most of which have a calcareous 

 covering, and all of which have a double circulation of sanies 

 or white blood, includes the Malacostraca, as the crab, lobster, 

 shrimp, and prawn, the squill, and the wood louse ; and the 

 Entomostraca, as the king or horseshoe crab, the fish louse, and 

 perhaps the fossil trilobite. The third class, Jlrachnides, breathing 

 by means of transverse air tubes, called stigmata, includes the Pul- 

 monariae, or the spider, tarantula, and scorpion ; and the Trachea- 

 riae, among which are the mite and the tick. The fourth class, 

 Insecta, breathing by means of two longitudinal air tubes, called 

 tracheae, and provided with antennae, horns or feelers, includes the 

 Myriapoda, or centipede, and scolopendra ; the Thysanoura, as the 

 podura ; the Parasita, as the louse ; the Suctoria, as the flea ; the 

 Coleoptera, as the water flea, snap bug, glow-worm, and firefly, the 

 grub, and the beetle, the cantharis or Spanish fly, the weevil fly, the 

 cow bug, and lady bug ; the Orthoptera, as the earwig, roach or 

 cockroach, cricket, and grasshopper; the Hemiptera, as the bed bug; 

 with the Homoptera, or locust, and cochineal insect; the Neuroptera, 

 as the dragon fly, ephemera or May fly, the lion ant, and white ant; 

 the Hymenoptera, as the saw fly, ichneumon fly, common ant, wasp, 

 and bee ; the Lepidoptera, or butterfly, moth, and silk worm ; and 

 the Diptera, or mosquito, crane fly, horse fly, gad fly, and the com- 

 mon fly. Many of these insects undergo transformations or meta- 

 morphoses ; taking, when first hatched, the form of larvae, as worms 

 or caterpillars ; which at length surround themselves with a web or 

 cocoon, and are then called pupse, chrysalides, anrelias, or nymphs ; 

 from which they finally emerge in their perfect state, many of them 

 with wings ; prepared to lay their eggs and' die. 



