. A manual of zoology. Zoology. GENERAL ORGANOLOGY 97 tissues is derived either from the air or from the water, according as the animal is terrestrial or aquatic. Less frequently it is the case that water- dwellers breathe air, and hence are compelled, from time to time to rise to the surface of the water for air; this is true for the large marine mam- mals, and for many insects, spiders, and snails found in fresh water. Air- and water-breathing takes place exclusively through the skin, so long as this is delicate and readily permeable and no higher development of organ- ization necessitates a
. A manual of zoology. Zoology. GENERAL ORGANOLOGY 97 tissues is derived either from the air or from the water, according as the animal is terrestrial or aquatic. Less frequently it is the case that water- dwellers breathe air, and hence are compelled, from time to time to rise to the surface of the water for air; this is true for the large marine mam- mals, and for many insects, spiders, and snails found in fresh water. Air- and water-breathing takes place exclusively through the skin, so long as this is delicate and readily permeable and no higher development of organ- ization necessitates a more active interchange. If the demand for oxygen. Fig. 62.—Left second foot of a cra}'fish with (br) attached gill (after Huxley). cxp, coxopodite; bp, basipodite; ip, ischiopodile; mp, meropodite; c/), carpopodite; pp, propodite; dp, dactylopodite; cxs, bristles of the coxopodite; e, lamina of the gill. be greater, special breathing-organs are found—gills {brandiicc) for water- breathing, lungs and trachece for air-breathing, in addition to which the skin functions as an accessory organ of more or less importance. Gills are usually thin-walled, frequently ciliated areas of the skin which are abundantly supplied with blood-vessels, and where richly branched tuftlike projections or broad leaves have grown out, thus furnishing the largest possible surface for the interchange of gases; these occur in such a position as to be most exposed to fresh water; in the crayfish, for example, they are on the legs, where the motion drives fresh 7. 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 Hertwig, Richard, 1850-1937; Kingsley, J. S. (John Sterling), 1854-1929, ed. and tr. New York, H. Holt
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
