THE SPERM-WHALE. 103 
is a greater disproportion of size between sexes than in any 
other known species of cetaceans. 
The form of the beast is without symmetry, and from the 
general absence of other prominent organs than the tail or 
pectoral fins, can be compared to little else than a dark rock or 
the bole of some giant tree. The prevailing colour is a dull black, 
occasionally marked with white, especially on the abdomen and 
tail. The summit of the head and trunk presents a plane sur- 
face, until about the posterior third of the back, whence arises a 
hump or spurious fin of pyramidal form, and entirely composed 
of fat. From this embossed appendage an undulating series of 
six or eight similar, but smaller elevations, occupies the upper 
margin or ridge of the tail to the commencement of the caudal 
fin. The pectoral fins or paddles are placed a short distance 
behind the head; they are triangular in shape, diminutive as 
compared with the size of the whale, and being connected to 
the trunk by a ball and socket joint, possess free movement, 
either vertical or horizontal. 
Owing to the flexibility of the tail, the movements of the tail- 
fin, or “ flukes,” which sometimes measures eighteen feet across, 
are exceedingly extensive, whilst its power may be estimated by 
the gigantic bundles of round tendons, which pass on either side 
the loins, to be inserted into its base. Whether wielded in 
sportive mood or in anger, its action is marked by rapidity and 
ease, and when struck forcibly on the surface of the ocean, pro- 
duces a report which may be heard at a considerable distance. 
In progression, the action of this organ is precisely the reverse 
of that of the tail of the lobster, for whilst the latter animal 
swims backward by striking the water with its tail from behind 
forwards, the cachalot and other cetaceans swim forward by 
striking with their flukes in the contrary direction, the fin being 
brought beneath the body by an oblique and unresisting move- 
ment; while the act of springing it back and straightening the 
tail propels the animal ahead with an undulating or leaping 
gait. When employed offensively the tail is curved in a direc- 
tion contrary to that of the object aimed at, and the blow is 
inflicted by the force of the recoil. The lower jaw appears 
diminutive, slender, and not unlike the lower mandible of a 
bird. When the mouth is closed it is received within the soft 
parts pendent from the border of the upper jaw, and is nearly 
