. Zoology. Zoology. 80 ZOOLOGY. Class I.âCeustacea {Water-fleas, Shrimps, Lobsters, and Crabs). General Characters of Crustaceans.âThe typical forms of this class are the craw-fish, lobster, and crab, which the student should carefully examine, as from them a general knowledge of the class, which varies greatly in form in the diSerent 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 Central and Western States. The lobster's body consists of segments, six of which in the abdo- men are seen to
. Zoology. Zoology. 80 ZOOLOGY. Class I.âCeustacea {Water-fleas, Shrimps, Lobsters, and Crabs). General Characters of Crustaceans.âThe typical forms of this class are the craw-fish, lobster, and crab, which the student should carefully examine, as from them a general knowledge of the class, which varies greatly in form in the diSerent 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 Central and Western States. The lobster's body consists of segments, six of which in the abdo- men are seen to form a complete ring, bearing a pair of jointed ap- pendages. Tlie abdomen consists of seven segments. One of these segments (Fig. 94, I)') should be sep- arated from the others by tlie student, in order to observe the mode of inser- tion of the legs. Each segment bears but a single pair of appendages, and it is a general rule that in the Arthropods eacli segment bears but a single pair of appendages. Tlie abdominal feet ,,â ,,, . , â J. Fig, 95âMandible of the lobster, are called swimmerets; they are Homarus americanus: pal. narrow, slender, divided at the end palpus, into two or three lobes or portions, and are used for swimming, as well as in the female for carrying the eggs. The first pair are slender in the female (Fig. 94, Bj) and not divided, while in the male (Fig. 94, Bs) they are much larger, and aid iu reproduction. The segment (Fig. 94, (?) bears broad paddle-like appendages, while the seventh segment, forming the end of the body and called the "telson," bears no appendages. It repre- sents the tergum alone of the segment. Turning now to the cephalo- thorax, we see that there are two pairs of antennae, the smaller pair the most anterior; a pair of mandiiiles with a palpus, situated on each side of the mouth; two pairs of ,' or accessory jaws, which are flat, divided into lobes, and of unequal size; three pairs of foot-jaws (maxilliped
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1897
