Entomology : with special reference to its biological and economic aspects . speciesof insect. Iron, manganeseand certain pigments also enterinto the composition of theintegument. Chitin is not peculiar to ar-thropods, for it has been de-tected in the setae and pharyn-geal teeth of annelid worms,the shell of Lingula and thepen of the cuttle fish (Kruken-berg). The chitinous integument (Fig. 88) of most insects con-sists of two layers: (i) an outer layer, homogeneous, dense,without lamella or pore canals, and being the seat of the cutic-ular colors; (2) an inner layer, thickly pierced with pore
Entomology : with special reference to its biological and economic aspects . speciesof insect. Iron, manganeseand certain pigments also enterinto the composition of theintegument. Chitin is not peculiar to ar-thropods, for it has been de-tected in the setae and pharyn-geal teeth of annelid worms,the shell of Lingula and thepen of the cuttle fish (Kruken-berg). The chitinous integument (Fig. 88) of most insects con-sists of two layers: (i) an outer layer, homogeneous, dense,without lamella or pore canals, and being the seat of the cutic-ular colors; (2) an inner layer, thickly pierced with porecanals, and always in layers of different refractive indices anddifferent stainability. (Tower.) These two layers, respec-tively primary and secondary cuticula, are radically differentin chemical and physical properties. The chitinous cuticulais secreted, as a fluid, from the hypodermis cells. Each layerarises as a fluid secretion from the hypodermis cells, the pri-mary cuticula being the first to form and harden. The fluid that separates the old from the new cuticula at. Section through integument of abeetle, CJirysoboihris. b, basementmembrane; c^, primary cuticula; c,secondary cuticula; h, hypodermis cell;n, nucleus.—After Tower. ANATOMY AND PHYSIOLOGY 75 ecdysis is poured over the hypodermis by certain large specialcells, which, according^ to Tower. are not true glands, butthe setigerous cells which, in early life, are chiefly concernedwith the formation of the hairs upon the body; but upon the Fig. 89. \ ^
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectentomology, bookyear1
