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Abstract
It is evident, that the wide apertures between the gills are closed in quiet respiration, during inspiration as well as during expiration, because the filament-tips of the posterior hemibranchia of each gill are in continuous contact with those of the anterior hemibranchia of the next gill. The communication between the inspiratory and the expiratory cavity is kept up by the narrow slits between the lamellae. The skeleton and the ligament apparatus of the filaments are constructed in such a way, that the normal position of abduction of both filament-rows of a gill is maintained in spite of the fact, that in both respiratory phases the pressure in the inspiratory cavity is higher than that in the expiratory cavity. The figures of gills of the Teleostei, which are found in different textbooks, show a wide aperture between the filament-tips of the hemibranchiae of two successive gills. In the living animal this wide communication between the inspiratory and the expiratory cavity does not exist in quiet respiration, but is only seen during the coughing movements. Small fragments of defilement, which are accumulated against the gills, are then removed and are spit out by the mouth (coughing in a forward direction) or appear from under the gill-cover with the respiratory water (coughing in backward direction). During coughing an adduction movement is seen of the filament-tips of the two hemibranchiae of a gill by the contraction of the adductor muscles. The adductor muscles do not act rhythmically. They play no part in the circulation of the blood through the branchial vessels (RIESS 1881, WOSKOBOINIKOFF 1932), nor in the renewal of the respiratory water (ELFRIEDE SCHÖTTLE 1932), but they are of significance for the cleaning of the gills by means of the coughing movements. During coughing the so-called abductor muscles probably prevent a caudal movement of the adducted filament-rows of a gill, by which the branchial apertures could be closed up. It is possible, that they act exclusively during coughing in a forward direction.