General principles of zoology . and for oxygen is greater,other more special breathing-organs are found—gills forwater-breathing, lungs and tracheae for air-breathing, inaddition to which the skin functions as an accessory organof more or less importance. Gills.—The gills are usually thin-walled areas of theskin which are particularly well supplied with blood-ves-sels, and where richly branched tuftlike projections or broadleaves have grown out, thus furnishing the largest possiblesurface for the interchange of gases; these lie in such aposition as to be most exposed to fresh water; in the GEN
General principles of zoology . and for oxygen is greater,other more special breathing-organs are found—gills forwater-breathing, lungs and tracheae for air-breathing, inaddition to which the skin functions as an accessory organof more or less importance. Gills.—The gills are usually thin-walled areas of theskin which are particularly well supplied with blood-ves-sels, and where richly branched tuftlike projections or broadleaves have grown out, thus furnishing the largest possiblesurface for the interchange of gases; these lie in such aposition as to be most exposed to fresh water; in the GENERA L ORGA NO LOG Y. 129 crab, for example, they are on the legs, where the motiondrives fresh water constantly through them (Fig. 58); inthe swimming worms, on the back; in the tube-dwellingworms, at the anterior end, projecting out of the tube; inmost amphibians, on each side of the head. More rarely thedigestive tract functions for water-breathing; in the fishes,Enteropneusta, and tunicatcs gills have been formed in con-. S5
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
