The Structure and Habits of Pliysalia. 367 



and captured both Pliysalia and fish in the small hoop casting-net 

 I was in the habit of using, that I can confidently state there 

 is no hostility between tnem under ordinary circumstances, 

 and that the mere contact of the fish with the tentacles of the 

 former does not result in any observable inconvenience to either 

 animal. The fish (according to Dr. Giinther, who very kindly 

 examined my sketch and favoured me with his opinion) is proba- 

 bly either a young form of one of the Sconib ridge, or, if mature, a 

 member of some unknown genus. It is curious, however, that the 

 specimens captured by me over a wide area of the Atlantic, 

 invariably belonged to the same species, and were, as nearly as 

 possible, of one size ; that is to say, from two to three inches 

 in length ; the colour on the back being a deep blue, identical 

 with that of the casnosarc and body of the polypites of 

 Pliysalia. Nor was this fish the only attendant on it ; for, 

 crawling about within the mass of polypites and tentacles, I as 

 often found several Isopod crustaceans, from a quarter to 

 three-quarters of an inch in length, evidently parasitic in this 

 position. The same species was also observed by me frequently 

 on the float of Ianthina, and on floating epiphytic Lepadidse. 

 Here, again, it is clear that the urticating organs are innocuous, 

 inasmuch as partially devoured or dead specimens were never 

 met with. 



Lastly, I have not observed the marked iridescent quality 

 which has been stated to accompany the brilliant tints of 

 the Physalidee. The colours themselves are extremely rich, 

 the contrast afforded by the roseate pink of the upper margin 

 of the crest, and the graduated tints of blue, commencing with 

 the faintest opalescence on the upper surface of the pneuma- 

 tophore, to the deep and almost full-toned indigo of the 

 csenosarc and appendages, being very striking. Intermixed 

 with these colours are the greenish streaks which mark the out- 

 lines of the cgecal chambers of the crest, and the root-like con- 

 tinuations of the velvety dark-coloured mass beneath. The 

 minute mammiliform protuberance at one extremity of the 

 pneumatophore is also of bluish green, whilst the walls of the 

 air cavity itself, although almost colourless, reflect the images 

 and tints of passing objects in the same manner as a soap- 

 bubble, but without any greater amount of iridescence than is 

 perceptible in ligament. 



Of the mode of development of the embryo and of the air- 

 chamber in the Physophoridas generally, nothing is at present 

 known ; the young Physalia having only been seen when already 

 so far advanced in growth as to constitute a nearly perfect, 

 though comparatively minute, individual. In like manner we 

 have still much to learn regarding the true basis of specific dis- 

 tinction in this class of organisms ; the older authors having 



