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THE ZOOLOGIST. 



and " two-winged," which, though not scientific, are commonly 

 understood ; each may include several species as known to 

 science. 



The " four-winged" fly with the ventral fins extended, hut 

 whether these vibrate like the pectorals I cannot say ; they 

 always appear to me to be motionless. In this group the 

 pectorals and ventrals are of an opaque indigo colour with 

 colourless, transparent patches at or near the insertions ; I have 

 also noticed the pectorals of some to be a dull ochre mottled 

 with dark spots. 



The " two-winged " fish are smaller, and do not apparently 

 extend the ventrals in flight ; both pectorals and ventrals are of 

 a very pale transparent blue tint. 



There are several circumstances which increase the difficulty 

 of observing the wing movement in flight. 



The fact that the fish is nearly always viewed from above 

 and that the light strikes on the glistening surface tends to 

 confuse the sight. On one voyage, however, I was able to watch 

 the flight from below, in very rough weather, from the deck of a 

 small tramp steamer in the Arabian Sea, and on this occasion 

 for several days I watched the flights, when the vibration of 

 both fins and tail was perfectly distinct. It was on this occasion 

 that I paid particular attention to the mode of flight for the first 

 time, because I had always read in " the books " that the fish 

 soared or sailed like birds, and was surprised to see anything 

 different. 



The unfamiliar direction of the vibration of the wings, which 

 instead of being up and down as in the case of birds is almost 

 horizontal, also tends to confuse the sight ; and the fact that 

 usually the flight is viewed from behind or nearly so (the worst 

 position for observation) must be remembered. On the com- 

 paratively rare occasions when I have seen Flying-Fish rise in 

 their flight towards the ship and fly on board towards me I 

 have clearly seen the flutter of their wings, although this has 

 generally happened as the light was failing ; mostly, of course, 

 they come on board in the dark. Moreover, the fish bursts upon 

 the sight suddenly from an unexpected spot, and so is some way 

 off before the observer can get a clear sight of the flight, just as 

 a bolting rabbit is out of range before the novice can get a 



