472 DR. E. H. HANKIN ON THE 



metres per second a.iul if their velocities tend to increase as soon 

 as tliey begin to glide downwards, it is obvious that they ninst 

 possess some means of checking speed. Otherwise the}' would be 

 unable to land without accident. In ' Animal Flight ' two methods 

 of checking speed, one used for high-speed flight, the other used 

 for low-speed flight, have been described. Two analogous methods, 

 for slow and fast speed respectivel}', employed by flying-fishes 

 have now to be described. 



5. Method of checking speed in high-speed flight. 



This method, which depends on changes of position of the hind 

 wings (pelvic fins), has only been followed by me in species whose 

 wings are coloured. It would be quite beyond my powers of 

 observation to see the adjustment in those species whose wings 

 are moi'e or less transparent. Of the species that have yielded 

 most opportunities for these observations may be mentioned one 

 with black hind wings and another whose hind wings have a 

 chocolate-brown colour. The observations about to be described 

 are very difiicult to make, and the follo\Aing account is, to some 

 extent, compiled from glimpses of parts of the adjustment seen 

 on difl'erent occasions. 



The flying-fish starts its flight with the hind wings directed 

 outwards and backwards and extended in the horizontal plane. 

 At some distance, perhaps 50 metres, from the end of its flight, it 

 may be seen suddenly to lower its hind wings (pelvic fins) so that 

 they point nearly vertically downwards. On my recent voyage, 

 when using a binocular of magnification 10. it appeared to me 

 that, when the hind wings are in the down position, their plane 

 is parallel to the direction of flight. In this position the leading 

 edge only of the hind wing would ofler direct resistance to speed 

 ahead. But on a voyage in 1914, when I was using an Aitchison 

 binocular of the very unusual magnification 25, on two occasions 

 the hind wings, when in the down position, appeared to me to be 

 slightly rotated round their long axis so that their hind margins 

 approached each other. On one of these occasions, during part 

 of the flight, one hind wing was less visible than the other. 

 This was probably due to its having been seen end on. When 

 the fish changed its course so that it was tra,veliing directly 

 away from me the two hind wings became equally visible. With 

 the hind wings thus disposed it is obvious th.at the air passing 

 between them must be,so to speak, entering a funnel, and therefore 

 much resistance would be oftered to speed ahead. It is probable 

 that these two dispositions of tlie hind wings are used successively, 

 for, within about a second of the end of the flight, the two hind 

 wings ai'e suddenly rotated through nearly a right angle round 

 their long axes. The result of this manreuvre is tliat the plane 

 of the hind wings acquires a, position at right angles to the 

 directio)! of tiight. In the first down position the hind w'ings are 

 not fully expanded. In the last position they are expanded to 



