266 By Stream and Sea. 



concerned, but not with respect to the lesser pair underneath. 

 But afterwards I formed a decided opinion that the creature 

 begins its career by a rapid motion of the wing-fins, and 

 that, having acquired the requisite momentum, it keeps them 

 fixed and outstretched until it touches water once more. 

 The following I quote as a technical description of the 

 flying fish's modus operandi: — 



" The principal external agents employed in this mode of 

 locomotion are the large lobe of the tail-fin and the broad 

 transparent pectoral fins, which on this occasion serve at 

 least as a parachute, and which, being situated close to the 

 back, place the centre of suspension higher than the centre 

 of gravity. It is also curious to notice how well the specific 

 gravity of the fish can be regulated in correspondence with 

 the element through which it may move. The swim bladder, 

 when perfectly distended, occupies nearly the entire cavity of 

 the abdomen, and contains a large quantity of air ; and in 

 addition to this there is a membrane in the mouth which can 

 be inflated through the gills; these two reservoirs of air 

 affording good substitutes for the air cells so freely distributed 

 within the bones of birds, and having the additional advan- 

 tage of being voluntary in their function. 1 ' 



Whether the occasional dipping of the fish into the sea as 

 it flies is an absolute necessity to further progress is also an 

 open question, but it would seem reasonable to suppose 

 that the delicate wing-fins outspread in the sun and wind 

 would soon become dry, and, like the throat of the orator, 

 require occasional moistening. The fish does dip, and 

 pretty often too, but, it struck me sometimes, not because 

 there was pressing occasion for it so much as because the 

 ridge of the billow afforded a passing temptation. Neither 

 could it have been for purposes of rest after exhaustion, since 

 there was no pause ; the fish on the wing simply brushed 



