. Text-fig. 2. A, View of the float from above, to show the angle from which B is seen. The apical pore end (dotted) has been removed at the level indicated by the broken line. The openings around the bulge region and the side lead into the groups of appendages. B, View into the interior of a float from which the apical pore end and the whole saccus has been removed. For convenience, the float and crest are drawn as if they were still supported from within by the saccus, but if an animal were actually opened in this way, the float would collapse completely. Note the vaulting in the roof, formi
. Text-fig. 2. A, View of the float from above, to show the angle from which B is seen. The apical pore end (dotted) has been removed at the level indicated by the broken line. The openings around the bulge region and the side lead into the groups of appendages. B, View into the interior of a float from which the apical pore end and the whole saccus has been removed. For convenience, the float and crest are drawn as if they were still supported from within by the saccus, but if an animal were actually opened in this way, the float would collapse completely. Note the vaulting in the roof, forming pockets into which the saccus outpushings would normally fit. The author's observations, considered in retrospect, support Totton's interpretation. It was several times observed that a sudden drop in the wind would cause sailing specimens of Physalia to fall over on to the windward side. Specimens were much less apt to fall on to their leeward sides; to do so would mean hauling a considerable weight of tentacles up out of the water. Bigelow (1891) was the first to draw attention to this fact. The float is precariously balanced, and slight local contractions of the muscular wall can bring about shifting in the centre of gravity and consequent rolling into a new orientation. Rolling occurs mainly about the a-b axis (Text-fig. 1), sometimes about the b-c axis. In the latter case, the apical pore end may rear up high in the air, and a complete somersault take place. These variations are understandable when one considers that all three sides of the float are contractile and that contraction can be localized in particular areas. A considerable range of body form can be assumed, in all of which the pattern of rolling will be different. It was found possible, by electrical stimulation of appropriate regions of the float wall, to evoke local contractions of sufficient power to bring about shifting of the centre of gravity and various kinds of rolling.
Size: 1769px × 2825px
Photo credit: © The Bookworm Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, booksubjectocean, booksubjectscientificexpediti
