File:Hardwicke's science-gossip - an illustrated medium of interchange and gossip for students and lovers of nature (1884) (14803112833).jpg

Identifier: hardwickesscienc20cook (find matches)
Title: Hardwicke's science-gossip : an illustrated medium of interchange and gossip for students and lovers of nature
Year: 1884 (1880s)
Authors: Cooke, M. C. (Mordecai Cubitt), b. 1825 Taylor, J. E. (John Ellor), 1837-1895
Subjects: Science Natural history
Publisher: London : Robert Hardwicke
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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of polygonal, nucleated cells,forming a mosaic pattern, but becoming irregular and The large tracheal tubes close to the spiracles are even branched in the finest branches. The cell-wallswithout spiral thread, and the intima is here sub- ; are hardly to be made out without staining. 206 HARDWICKES SCIENCE-GOSSIP. Externally, the chitinogenous cells rest upon adelicate basement-membrane. Where a number of branches are given off togetherthe tracheal tube may be dilated. Fine branches,such as accompany nerves, are often sinuous. Inthe very finest branches the tube loses its thread, thechitinogenous cells become irregular, and the intima border, which protects the opening. The air-tubedivides into two primary trunks immediately withinthe orifice. The second thoracic spiracle is simplerand smaller ; its valve is nearly semicircular, and theorifice, when slightly open, has the figure of a horse-shoe. The abdominal spiracles are obliquely trun-cated papilla; without valves and directed back-
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Fig. 122.—Tracheal System of Cockroach. Side view of head seen fromwithout, introducing the chief branches of the left half. X 15. Fig. 124.—Second Thoracic Spiracle of Cockroach (left side). X about 35. is lost in the nucleated protoplasmic mass whichreplaces the regular epithelium of the wider tubes.* The spiracles of the cockroach offer much intricatedetail, and it is far from easy to master their structureand mode of action. The first thoracic spiracle isthe largest in the body. It is closed externally by alarge, slightly two-lobcd valve, attached by its lower * It has been supposed that these irregular cells of thetracheal endings p.ass into those of the fat-body, but the lattercan always be distinguished by their larger and more sphericalnuclei. wards; their openings are vertical, and oval orelliptical. We have already pointed out that the wall of theair-tube for a .short distance from the spiracularorifice has a tesselated instead of a spiral marking.The tesselated border i

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