Wlarvels of the Universe 623 
SOME MARVELS OF FISH LOCOMOTION 
BY W. P. PYCRAFT, F.Z.S. 
EVEN among fishermen it is generally believed that a fish, in swimming, is propelled by its fins ; yet, 
with certain exceptions to be described presently, this is never the case: the fins serve merely as 
balancers, steering organs 
and brakes. Locomotion 
is performed by more 
or less rapid side-to-side 
movements of the tail, 
which, be it noted, repre- 
sents all that portion of 
the body lying behind 
the vent. The so-called 
“tail” is really the tail 
jin, which, though an 
important steering organ, 
does not, as we have re- 
marked, serve to propel 
the body. 
Now, as to these ex- 
ceptions: though few in 
number, they are cer- 
tainly remarkable in kind. 
Most of these swim by 
means of the dorsal or 
back fin, which by ex- 
cessively rapid vibrations 
acts as a propeller, driv- 
ing the body through the 
water. In many such 
cases ;the body is of a 
most extraordinary shape, 
being about twice as 
deep, as it is long; that 
is to say, the length 
from the snout to the 
fork of the tail fin is 
only about half the 
height! In some cases, 
as in the Sail-fish, this 
depth is formed by the 
pacman y Jevelopment ot Sun-fishes depend largely for food on prey caught at enormous depths; especially are they 
the dorsal fin and its partial to larval eels, which can only be had by diving; hence their grotesque appearance and 
corresponding fin of the the adaptation of the dorsal fin for progression by means of vibration. 
under surface of the body—the “anal” fin. In others, as in the Sea-bat, the body itself is 
expanded. Now if the details of these curious fishes are for the moment ignored, and 
attention be concentrated on their general outline, it will be found that it makes a rough 
approximation to that presented by the grotesque-looking Sun-fishes, which have the 
THE SUN-FISH. 
