The gas bladder as a hydrostatic organ in Thymallus thymallus L., Osmerus eperlanus L. and Mallotus villosus Müll

Abstract

1. The gas bladder of Thymallus thymallus is investigated concerning\nthe topography, vascularization, histology and histochemistry. Simple\nmicro-retia mirabilia are found, forming a counter-current vascular system\nof probably very low exchange capacity. The epithelium, lining the lumen,\nis probably one of very low activity. If a secretion of gases into the bladder\noccurs, it is probably very slow.\n2. The gas bladder of Osmerus eperlanus is investigated as described\nabove. The blood vessels are not arranged as a counter-current system,\nthough capillaries reach the base of the epithelium. The epithelium,\nwhich is also EM investigated, contains apically considerable amounts\nof mucopolysaccharides and glycogen. A secretion, directly to the lumen,\nof gases or of a matter which can be transformed into gases, is proposed.\n3. The gas bladder of Mallotus villosus is investigated as described\nunder point 1. Besides, low power electron micrographs has been studied,\nand analyses of the gaseous content of the bladder were made after\nadministration of pilocarpine, dibenzyline and yohimbine. No counter\ncurrent vascular system is present but capillaries reach the base of the\nepithelium. The epithelial cells contain and probably secrete polysaccharides\n(though not glycogen) directly to the lumen. The gas is composed\nof 0-2% carbon dioxide, 0-18% oxygen and 80-100% inert gases.\nThe administration of drugs did not in any case increase the percentage\nof oxygen or carbon dioxide, compared with the control animals. It\nis proposed that no gas secretion occurs.\n4. The muscle layer of the gas bladder is in all the three species\ncontinuous with the muscularis externa of the oesophagus. This argues\nfor a neutral terminology concerning the layers of the gas bladder wall.\n5. A muscular sphincter is morphologically documented at the debouch\nof the pneumatic duct into the oesophagus.\n\nSupported by grants from the Faculty of Mathematics and Science\nof the University of Lund. Photos by B. Henriksson.