Dr. W. G. Ridewood on Jflying-jUhes. 5-47 



For the purpose of this comparison spirit-preserved 

 specimens of Exoccetus evo/ans and Hemirhamphus roberti 

 were taken, of as nearly the same size as was possible. 

 Hemirhamphus is a more slender fish than Exoccetus, the 

 lower lobe of its caudal fin is only slightly larger than the 

 upper lobe, and the lower jaw is greatly produced beyond 

 the upper jaw. For comparing the lengths of the two fishes, 

 therefore, it is better to disregard the lower jaw and the tail- 

 fin, and to measure from the front of the upper jaw to the 

 end of the scaly part of the base of the tail. This measure- 

 ment in the case of Exoccetus was 151 mm.; in Hemi- 

 rhamphus it was 185 mm. The length of the pectoral fin 

 lying closed against the side of the body was 106 mm. in 

 Exocatus ; in Hemirhamphus it was 23 mm. The girth of 

 the middle part of the body was 81 mm. in Exoccetus and 

 71 mm. in Hemirhamphus. In the case of Exoccetus the 

 weight of the body was 46*5 grammes, the weight of the 

 right and left external pectoral muscles "78 gramme, and 

 the proportion yielded was 1 to 59*61. In the case of Hemi- 

 rhamphus the body-weight was 39*0 grammes, the weight of 

 the external pectoral muscles "32 gramme, and the propor- 

 tion was 1 to 121*87. Or, putting it the other way, the 

 body-weight in each case being unity, the pectoral muscle- 

 weight is "0167 of the body-weight in Exoccetus and "0082 in 

 Hemirhamphus. In other words, the muscles are twice as 

 large in Exoccetus as in a Hemirhamphus of about the same 

 size. 



That the pectoral fins of Exoccetus are larger than in most 

 fishes of the same size is admitted by all, even by those who 

 contend that the fish does not fly, i. e. flap its fius, but 

 merely uses the fins for gliding or " planing" when once the 

 vigorous lashing of the tail has jerked the body obliquely 

 into the air. With an enlargement of the fin-area one 

 would naturally expect an enlargement of the muscles that 

 operate the fius. The point to be solved is whether the 

 muscles have been enlarged in the same proportion as the 

 fin-area, or whether they have been enlarged in a much 

 greater proportion, as would be necessary if the fish is to 

 flap the fins so vigorously as to maintain the body in the air, 

 as is claimed by the adherents of the " flying " hypothesis. 



For the determination of this point the left pectoral fin of 

 each rish was spread out on a sheet of paper, a pencil line 

 was drawn around the edge, and the paper was then cut 

 along the pencil line. A strip of the same sheet of paper 

 was cut 1 centimetre wide, and this strip was shortened 

 successively until it weighed the same as the piece of paper 



