. The comparative physiology of respiratory mechanisms. Respiration. TRACHEAL RESPIRATION 121 show how important it is for many insects to keep down the water loss, demonstrate the increase when the spiracles are forced open, and point out the almost complete impermea- bility of the integument of many insects to water Tod™? 30 20 W 8 ID 12 Weeks B Fig. 67. The effect of opening the spiracles on the rate of loss of water. A, rate of loss from a starving mealworm; B, rate of loss from a number of fleas in 1/100 mg per mg per hour. Columns marked x obtained when the spiracles were kept o
. The comparative physiology of respiratory mechanisms. Respiration. TRACHEAL RESPIRATION 121 show how important it is for many insects to keep down the water loss, demonstrate the increase when the spiracles are forced open, and point out the almost complete impermea- bility of the integument of many insects to water Tod™? 30 20 W 8 ID 12 Weeks B Fig. 67. The effect of opening the spiracles on the rate of loss of water. A, rate of loss from a starving mealworm; B, rate of loss from a number of fleas in 1/100 mg per mg per hour. Columns marked x obtained when the spiracles were kept open with 5% CO.,. (Mellanby.) The experiment illustrated by Fig. 67 is very convincing. The curve shows the rate of water loss from a fasting mealworm over 18 weeks. It is gradually reduced with the falling metabolism, but when the animal was forced by C02 to keep its spiracles open (at X in the figure) the evaporation rose to a high level, nearly the same after sixteen weeks as after two. By the mechanism now described, diffusion can only be regulated downwards. Wigglesworth has discovered another mechanism by which the insect can meet increased demands and which is in its effects analogous to the opening up of capillaries in active muscles in vertebrates. This mechanism is located in the non-chitinous tracheoles of less than 1 micron diameter which branch out from the smallest tracheae and form a rich network1 surrounding cells or penetrating into them, as in flight muscles where the tracheoles may even invest the single fibrils and sarcomeres. These final branches are normally invisible in the living insect, because they are filled with fluid, and the central point in 1 It seems difficult to decide whether true networks exist or the final branches have free endings. In several cases where loops have been described, , in the tracheal gills of Odonata (fig. 83), a closer investigation has shown that each tracheole ends by itself. From the point of view of oxygen supply t
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Keywords: ., bookcentury1900, bookcollectionbiodivers, booksubjectrespiration
