. An introduction to zoology : for the use of high schools . ght innumber in the catfish, but frequently absent in other forms. 5. In most fishes the skin is strengthened by bony scales,either round in outline—cycloid—or with the hinder margintoothed—ctenoid—(Fig. 2), bui the catfish is destitute ofsuch, except for certain very minute ones which are in thewalls of the lateral canal. The skin is therefore soft andslip[)ery, and variously coloured according to the distributionof pigment in it. It is tightly bound down to the underlyingflesh by slips of fibrous tissue, but in certain parts some l
. An introduction to zoology : for the use of high schools . ght innumber in the catfish, but frequently absent in other forms. 5. In most fishes the skin is strengthened by bony scales,either round in outline—cycloid—or with the hinder margintoothed—ctenoid—(Fig. 2), bui the catfish is destitute ofsuch, except for certain very minute ones which are in thewalls of the lateral canal. The skin is therefore soft andslip[)ery, and variously coloured according to the distributionof pigment in it. It is tightly bound down to the underlyingflesh by slips of fibrous tissue, but in certain parts some loosesubcutaneous tissue is accumulated between them. When asharp cut is made through the skin it is possible to recognizetwo layers, an outei, the epidermis and an inner, the cerium, HIGH SCHOOL ZOOLOGY. 13 which layers indeed exist in tlie skin of all Vertebrates. Jt ischiefly but not exclusively in the latter that the pigment iscontained. If the epidermis be removed by scraping, the ex-posed surface of the corium will be observed to be rough with. A. B. Fiy. 2. —A, Cycloid Scale from Lake Hcrrinf,. B, Ctenoid Scale from Rock Bass. /j. papillae, so that the smoothness of the surface is due tothese interpapillary spaces being filled up with the papillae are of importance as the channels through whichnerves and nutriment from the blood-vessels reach the epidermisfiom the corium. 6. Minute Structure of the Skin. General Remarks on Histology.—That branch of the study of thestructure of animals which deals with the minute elements of the variousorgans, and which requires the microscope and other tools in tlie courseof its investigations, is termed Histology. Each organ of the bodyis built up of tissues, and each tissue is formed of ultimate elementsnamed cells arranged in a characteristic way. Thus the skin, which isa complicated organ performing very different functions, is comjjosedchiefly of two kinds of tissues—the epithelial tissue of the epidermis,
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1889
