certain associated Scombroid Fish. 9 



But the most singular phenomenon connected with Physalia 

 consists in its power of slowly and steadily depressing its pneu- 

 matophore from its normal erect position to a position which is 

 horizontal, or, in other words, till the pneumatophore rests on 

 one of its sides on the surface of the water. The act of eleva- 

 tion or depression occupies from eight to ten seconds or there- 

 about, and takes place as soon as the creature comes abreast of 

 the bows of the ship, the state of depression continuing until 

 it is abreast of the stern. I have so repeatedly witnessed this 

 wonderful occurrence in moderately calm weather, at distances 

 varying from a few feet to thirty or even fifty yards, that I 

 should feel inclined to attribute it to some subtle influence 

 produced either by molecular vibration in the water during the 

 transit of the vessel, or to some equally subtle vibration com- 

 municated to the pneumatophore through the intervening 

 atmosphere. The last, however, is, in all probability, the 

 most rational way of accounting for it, inasmuch as the com- 

 mencement of the depression takes place, in many instances, 

 apparently quite beyond the reach of the surface-disturbance of 

 the water, which causes a series of advancing waves ahead of 

 the ship. 



I would also take the opportunity of confirming what Mr. 

 Collingwood says regarding the small fishes which he saw 

 accompanying Physalia^ having not only observed them over 

 and over again, but captured them in some numbers in my 

 casting-net thrown from the main-chains or the main-gangway 

 port. Indeed, in a paper communicated by me, in December 

 1862, to ' The Intellectual Observer,' I distinctly drew atten- 

 tion to this fact, and mentioued that, having submitted some 

 sketches of the fish to Dr. Gunther of the British Museum*, he 

 expressed his opinion that, if mature fish, and not young 

 Scombridas, they belong in all probability to some new and 

 unknown genus. As these fish vary in size within very re- 

 stricted limits only (I have never seen one longer than 4 or 

 shorter than 3 inches t)> Dr. Glinther's suggestion as to their 

 being new to science is doubtless correct. 



As recorded by me, in the paper above referred to, these 

 fish accompany Physalia just as the pilot-fish accompany the 

 shark — in this instance swimming backwards and forwards 

 and amongst the tentacles in such a fashion as to suggest a 

 " co-operative " action between the two creatures, which re- 

 sults probably in a supply of food. I may add that, on many 

 occasions, I have also detected, adherent or creeping amongst 



* These sketches are now in the possession of the Microscopical Society. 

 t Mr. Collingwood speaks of having seen them 6 inches in length 

 (' Annals ' for November 1867). 



