Discovery reports (1962) Discovery reports discoveryreports30inst Year: 1962 3i° DISCOVERY REPORTS behaviour said, '. .. I have over and over again watched the operation going on with great vigour in a dead calm'. Floatation: Pneumatocyst or Air-sac I was surprised, when I first dissected a live Physalia by making a vertical cut with scissors down the outer pneumatocodon wall, to see how quickly this muscular coat retracted and freed the pneumato- cyst ; and particularly to see the branching digitiform processes of the latter which fit into the pockets of the crest. Because little attention
Discovery reports (1962) Discovery reports discoveryreports30inst Year: 1962 3i° DISCOVERY REPORTS behaviour said, '. .. I have over and over again watched the operation going on with great vigour in a dead calm'. Floatation: Pneumatocyst or Air-sac I was surprised, when I first dissected a live Physalia by making a vertical cut with scissors down the outer pneumatocodon wall, to see how quickly this muscular coat retracted and freed the pneumato- cyst ; and particularly to see the branching digitiform processes of the latter which fit into the pockets of the crest. Because little attention seems to have been paid to them, I give a photograph (PI. X, fig. 7) of a fixed specimen. To obtain fixation of the extended air-sac, which is covered inside, except for the area of the gas-gland, by a thin chitinous layer, it is necessary to maintain pressure for some time on the sac while it is in the fixative. The raising and lowering of the crest evidently depends on muscular compression and relaxation of the float and the air-sac, as described by Leuckart (1851). Lesson (1843) gave a crude figure (M, pi. 11). Text-fig. 1. Physalia physalts. A right-handed specimen, number 58, x | (Discovery St. 3255). Plan-view from above to show the septa of the crest. I, II = cormidia I and II (main zone). The textbook account of Physalia by Delage and Herouard (1901) contains statements—no autho- rity quoted—about crest-structure which need correction. First of all I have never seen any sign of an internal longitudinal septum in the crest. Secondly there is no perforated septum joining the edges of the primary and secondary septa, and partially enclosing the outer pockets of the pneumatocodon. In consequence it is untrue to say that the finger-like processes of the saccus form horizontal pairs, one on each side of a longitudinal septum. The authors also wrongly describe the gas-gland as strip- shaped: it is nearly circular. Their diagram of the relationship between crest-pockets
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