Image from page 175 of "The animans and man; an elementary textbook of zoology and human physiology" (1911)
Publisher: New York, H. Holt and company
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library
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s or boards,on damp soil, etc. They run aboutquickly, and feed chiefly on decayingvegetable matter. They are night-scavengers. Although commonly calledbugs and supposed to be insects,they really belong to the Crustacea,that class of animals which includesFIG. 63. A damp-bug, the crayfish, lobster, and crabs. Ex-Isopod. (Four times amine the body of a dead pill-bug. It is oval and convex above, rather pur-plish or grayish brown, and smooth. Note its division intohead, thorax, and abdomen. Find the eyes, the antennae, andthe mouth-parts. All the locomotory appendages are adaptedfor walking or running, not swimming. How many pairsof legs are there? Find gills and gill covers. Although thepill-bugs do not live in the water they breathe partly atleast by means of gills (though they may breathe partlythrough the skin). It is therefore necessary for them tolive in a damp atmosphere, so that the gill membranesmay be kept damp. If these are not moist, they will notpermit the exchange of gases.
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ARTHROPODS AND MOLLUSCS 155 Millipeds and centipeds (class Myriapoda).—The Myria-poda are land-animals breathing by means of trachea?like the insects. In them the body-segments are nearlyuniform in character with the exception of the head, which,as in the insects, bears the mouth-parts and antennae. Thereis no grouping of the body-segments into regions except as the head is distinct from the rest of the body. (In a few myriapods there are indications of a division of the hind body into thorax and abdomen.) The presence of true legs on all the
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