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 

 oompared 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 



