. The comparative physiology of respiratory mechanisms. Respiration. A42 Fig. 65. Structure of tracheae. A, close to spiracle. B, small branch more highly magnified, a epicuticle with spiral folds, d epithelial matrix. (Weber.) of tracheae branch out to the organs in the corresponding segment or segments. The spiracles are connected lengthwise by tracheal tubes, but these are of secondary importance only. The tracheae are circular in cross section with chitinous walls fortified by a spiral fold as shown in Fig. 65. They branch fairly regularly and the ag- gregate cross section remains very nea
. The comparative physiology of respiratory mechanisms. Respiration. A42 Fig. 65. Structure of tracheae. A, close to spiracle. B, small branch more highly magnified, a epicuticle with spiral folds, d epithelial matrix. (Weber.) of tracheae branch out to the organs in the corresponding segment or segments. The spiracles are connected lengthwise by tracheal tubes, but these are of secondary importance only. The tracheae are circular in cross section with chitinous walls fortified by a spiral fold as shown in Fig. 65. They branch fairly regularly and the ag- gregate cross section remains very nearly constant in the repeated branchings. The finest chitinous branches are continued in extremely nu- merous and narrow "trach- eoles" which are non-chitin- ous. All the tracheae are very resistant against pres- sure, which will produce only a slight shortening of the stems and branches. In these animals there are no specific respiratory movements, and the pressures set up in the body fluids by locomotion or even by violent struggling can cause ventilations only which are too small to be significant. When the average length of the tracheae and their aggregate cross section is made out it becomes possible to calculate the pressure difference necessary for a certain amount of oxygen, corresponding to the metabolism of the animal, to diffuse from the atmosphere to the tracheoles. Measurements made on the tracheal system of a large Cossus larva gave an aggregate cross-sectional area of all the tracheae supplying the tissues of mm2 with an average length of 6 mm. Through a tube of these dimensions the oxygen necessary for the animal's metabolism, viz., mm3/second, will diffuse by a pressure difference of 11 mm,1 which means that diffusion is ample to 1 The diffusion rate for CO2 in air is slightly lower, and the same quantity would require a pressure difference of 13 mm. The CO2 produced is on an average somewhat less than the oxygen used up, and 10 to 25% are elim
Size: 1118px × 2236px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionbiodivers, booksubjectrespiration
