SHARK. 
25 
amounts to the circumference of a circle, whose diameter is that of 
the portion of the ball comprehended within their points of insertion. 
This organisation seems necessary in the shark, which takes its prey 
by turning on its back, to enable it to keep its object in view when 
preparing to seize it. The eye balanced on a pivot is obviously 
capable of a greater extent of motion, in any direction, than when 
imbedded in the gelatinous matter, which lines the eye-sockets of 
most other fish. 
With the shark I obtained a specimen of the sucking fish, (Eche- 
neis Remora,) which I mention chiefly to remark, that it adheres as 
strongly to any surface when dead as alive. It is very difficult to 
remove it from any body to which it is applied, by pulling it perpen- 
dicularly, or backwards, but it readily yields when drawn off in the 
direction of its head. On examining its organ of adhesion with a 
lens, the cause of this readily appears. The plates composing it, 
which look single and membranous to the naked eye, under a micros- 
cope are seen to be divided each into several smaller plates, and 
armed with a row of fine teeth directed backwards. I was not sur- 
prised that its English name had produced a steady belief in some 
of my ship-mates, that it derived nourishment from the shark to 
which it adhered. 
This fish has no air-bladder, and must therefore (as its fins and 
tail are small) depend chiefly on the animals to which it is attached 
for progressive motion. For the same reason it cannot go in 
search of food, but must depend on something that passes near it for 
subsistence. The stomach of the specimen which I examined 
contained some filmy matter which looked like the remains of 
zoophytes. 
These notices may appear of little importance. I insert them 
from the conviction, that if every observation was recorded which 
has been made on the structure and habits of rare animals by those 
who have seen them alive, and in their native climates, much valuable 
information would now exist which is lost to the world. I know 
from experience, that many individuals of a ship are often well qua- 
E 
