. The comparative physiology of respiratory mechanisms. Respiration. 132 RESPIRATORY MECHANISMS that this increase is instantaneous and that the resting fre- quency and depth is restored immediately when the flight stops, and concluded, no doubt rightly, that no chemical but a purely reflex mechanism must be involved. Adaptation of tracheal respiration to an aquatic existence. Among the higher vertebrates respiring by lungs we found a small number of forms which had secondarily taken to the water and developed the necessary adaptations, all of them practically along the same line, returning to
. The comparative physiology of respiratory mechanisms. Respiration. 132 RESPIRATORY MECHANISMS that this increase is instantaneous and that the resting fre- quency and depth is restored immediately when the flight stops, and concluded, no doubt rightly, that no chemical but a purely reflex mechanism must be involved. Adaptation of tracheal respiration to an aquatic existence. Among the higher vertebrates respiring by lungs we found a small number of forms which had secondarily taken to the water and developed the necessary adaptations, all of them practically along the same line, returning to the surface at intervals to breathe. Among the tracheates a fairly large number have become aquatic, but, partly owing to their small size, they have been able to solve the respiratory problems in the most diverse ways. In one point, however, they have proved in- ferior to the aquatic vertebrates, they have not been able to invade the oceans, and only very few can exist in brackish water. Respiration at the surface by diffusion. In the simplest type of adaptation—from a physiological point of view—air-breathing through spiracles is retained. The functional spiracles are. Fig. 75. A, hydrophile hair in the water surface, seen in cross-section. A', position of equilibrium; B, hydrophobe hair in surface; B', equilibrium; C, spiracle surrounded by hydrophobe hairs (Stratiomys), position of equilibrium below surface; D, reaching surface; E, in equilibrium; F, short hydrophobe hairs on ventral cuticle of Dytiscus; G, curved hydrophobe hairs in Elmis and Harmonia. (Wigglesworth.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Krogh, August, 1874-1949. Philadelphia, University of Pennsylvania press
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