BEHAVIOUR 375 



In the laboratory, the animals' own efforts are not always sufficient to achieve righting; in the natural 



environment, however, wave action may assist the process as in Porpita (Mackie, 1959). One laboratory 



specimen made unsuccessful attempts at righting for more than 10 min. The attempts occurred at 



intervals of 25-35 sec. 



The righting activity, whether successful or not, consists of leeward side contractions. The repeated 

 performance of righting movements may be of assistance in developing the asymmetry of the young 

 animal. It is not known how the primary asymmetry arises, but it is a reasonable assumption that 

 once a leeward side and a windward side have been established, however tentatively, the normal 

 activity of the float will tend to fix and even to enhance it. 



The contraction of the codon musculature during the righting movements is not a smooth, steady 

 increase in tension; it is a succession of jerks, sometimes barely perceptible, which follow one another 

 at intervals of i|-2 sec. After each jerk there is some slight relaxation of the muscle, but this is more 

 than made good by the next jerk. In most specimens where rolling-behaviour was studied, five or six 

 jerks were sufficient to bring about the necessary degree of contraction for righting to take place. In 

 the specimen referred to above, which had difficulty in righting, ten or fifteen jerks were observed in 

 each unsuccessful attempt. If a kymograph record of the reaction could be obtained, the tracing 

 would be a 'staircase'. We are probably dealing with a phenomenon in the same class as the stepped 

 contraction of the sphincter-muscle of Calliactis, or of the circular swimming-musculature of Amelia. 

 Such responses are explained on a basis of neuromuscular facilitation (Pantin, 1935). 



3. Behaviour of the tentacles 

 In a medium-sized Physalia (gas-gland diameter = 1-4 cm.) observed when sailing freely outside the 

 harbour at Arrecife, the longer tentacles were found to extend to distances of 8-10 m. Following 

 stimulation of the float, the tentacles were drawn in, achieving what appeared to be full contraction 

 after about 1 min. The tentacles then measured 12-15 cm. These findings accord with Parker's 

 statement that a tentacle may contract to 1/70 its full length (Parker, 1932). 



As it contracts, a tentacle is thrown into lateral loops and then into primary and secondary coils. 

 The coiling seems to be a straightforward mechanical accompaniment of shortening, and is not to be 

 thought of as a device for ensnaring prey. The tentacles cannot 'writhe' or wrap themselves actively 

 round objects. The prey is secured to them solely by the nematocyst-filaments, acting as 

 harpoons. 



The process of fish-capture has never been closely observed in natural conditions, although 

 specimens holding prey in their tentacles have been studied in the laboratory (Wilson, 1947). Under 

 normal environmental conditions, contact of a tentacle with any solid object such as a fish will pre- 

 sumably evoke nematocyst discharge. The object, if animate, will suffer a temporary paralysis from 

 the action of the toxic substance in the nematocysts. It will be held against the tentacle by the 

 'nematocysts, and its weight, or the increased drag it causes, will stretch the tentacle and thus evoke 

 contraction. Gradually the fish will be brought up to the region of the gastrozooids which will apply 

 themselves to it, and begin to digest it. 



Laboratory observations made in the Canary Islands suggest that any abrupt mechanical stimulation 

 applied to the tentacles, whether causing stretching or not, will evoke contraction. For instance, it 

 was observed that a captured fish would be held passively in the tentacles for quite a long time unless 

 it became active, and struggled to escape. If this happened, the tentacles would begin to shorten 

 again. Any tactile stimulus, such as pinching with forceps, or striking with a glass rod caused some 

 degree of contraction either local or general. Bigelow (1891) found that there was little, if any, sensi- 

 tivity to food substances in solution. 



