364 The Structure and Habits of Physalia. 



which must become more or less parched by the fierce rays of 

 the tropical sun, — or a few lazy oscillations in answer to the 

 never-ceasing swell of the ocean. These are the only move- 

 ments which present themselves during calms, but a far more 

 remarkable phenomenon has repeatedly been noticed by me in 

 moderate weather when the ship is passing along at a speed 

 of not more than three or four knots an hour, and its im- 

 petus is sufficient to transmit delicate undulations for some 

 distance along the surface of the water, although there is 

 not sufficient wave-action to interrupt observation. Under 

 these circumstances, each Physalia, as it comes abreast of the 

 ship, even when at a distance of from thirty to sixty yards, 

 gently inclines its pneumatophore and crest to one side so as 

 to rest laterally on the water, and only regains its original 

 posture when the ship has advanced far enough to prevent the 

 transmission of the undulations. That the sensibility to the 

 mechanical disturbance thus produced at the surface of the sea 

 must be intensely acute is evident, inasmuch as the effect is 

 visible far beyond the range of any surface disturbance observ- 

 able by the eye. Hence it would seem to be aroused, not by 

 the ordinary wave-action by which the creature happens to be 

 surrounded, but by the subtle abnormal character imparted to 

 that action by the passage of the ship. It is hardly necessary 

 to state that, since no nervous system can be detected in the 

 Physalidse, there are, at present, no data even for speculation 

 on the physiological aspect of this highly curious phenomenon ; 

 and it must be obvious that any attempt to account for it on the 

 supposition that the acts in question are the result of direct 

 mechanical irritation, is simply substituting one unexplained 

 fact for another. At present, therefore, I have only to record 

 the act of the " Portuguese man-of-war " as one of very fre- 

 quent occurrence, leading it to more imaginative minds to trace 

 back the existing mode of salutation between vessels at sea 

 designated " dipping the colours," to this primaeval source. 



According to my own experience, the Physalidas never sink 

 below the surface as has been asserted, but merely become 

 lost to sight in the wave- disturbance when the weather is 

 stormy ; their peculiar colour and bubble-like aspect causing 

 them to be undistinguishable from the element by which they 

 are surrounded when at any distance from the observer's eye. 

 This view derives confirmation, moreover, from the fact that 

 they are frequently entrapped by the towing-net when not a 

 single specimen can be seen, owing to the reason assigned. 



The inclination to one side and re-erection of the pneuma- 

 tophore, to which reference has been made, is slowly performed, 

 (each operation occupying from three to five seconds) and would 

 seem to be effected by the contraction of the muscular wall on 



