. Zoology : for students and general readers . Zoology. 286 ZOOLOGT. Articulata of Cuvier as a heterogeneous assemblage of forms embracing at least three branches of the animal king- dom, namely, the Vermes, Tunicata, and Arthropo- da. The Arthropoda are di- vided into two well-de- fined classes, i. e., the Crustacea with two body- regions, the head-thorax a, and abdomen (Fig. 325), and breathing through the body-walls or by external gills; and the Inseda (Ti'a- cheata), in which the arthromeres are grouped into three body-regions, i. e., a head, thorax, and abdomen ; and which breathe by inte
. Zoology : for students and general readers . Zoology. 286 ZOOLOGT. Articulata of Cuvier as a heterogeneous assemblage of forms embracing at least three branches of the animal king- dom, namely, the Vermes, Tunicata, and Arthropo- da. The Arthropoda are di- vided into two well-de- fined classes, i. e., the Crustacea with two body- regions, the head-thorax a, and abdomen (Fig. 325), and breathing through the body-walls or by external gills; and the Inseda (Ti'a- cheata), in which the arthromeres are grouped into three body-regions, i. e., a head, thorax, and abdomen ; and which breathe by internal air-tubes (tracheas).. Fig. 225.—Common Shrimp, Crangon. cephalo-thorax; b, abdomen. Class I.—Crustacea {Water-fleas, Shrimps, Lohsters, and Crabs). General Characters of Crustaceans.—The typical forms of this class are the craw-fish, lobster, and crab, which the student should carefully examine as standards of comparison, from which a general knowledge of the class, which varies greatly in form in the different orders, may be obtained. The following account of the lobster will serve quite as well for the craw-fish, which abounds in the rivers and streams of the Middle and Western States. The body of the lobster consists of segments {somites, arthromeres), which in the abdomen are seen to form a com- plete ring, bearing a pair of jointed appendages, which are inserted between the sternum and tergum, the pleurum not being well marked in the abdominal segments. The abdo- men consists of seven segments. One of these segments (Fig 226 £)') should be separated from the others by the stu- dent, in order to observe the mode of insertion of the leg's. Bach segment bears but a single pair of appendHges, and it. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Packard, A. S. (Alpheus Spring), 1839-1905. New
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
