THE SPERM-WHALE FAMILY. 



15 



. The roof of the mouth, eV'en in the embry- 

 onic condition, is marked with numerous 

 transverse folds, such as are found also in 

 many other cetaceans, and in general in most 

 mammals. Only in the group with which we 

 are now dealing these folds are very numer- 



ous and covered with a thick horny epithelium. 

 During the growth of the young animal this 

 horny epithelium goes on developing. It 

 grows down on both sides in the form of a 

 fringe, and at last forms triangular transverse 

 plates, which are attached to the roof of the 



^ 



Fig. 142. —The Rorqual (Balcenoptcra boops). page 16. 



mouth by the small grooved edge, while they 

 present to the exterior a firm, slightly curved 

 edge, and on the interior are broken up into 

 a number of cylindrical fibres, the ends of 

 which form the third side of the triangle 

 which slopes away from the middle line of 

 the palate towards the outer edge of the 

 mouth. Into the above-mentioned groove on 

 the upper edge of each of these plates there 

 sinks a fold of the mucous membrane, which 

 is richly charged with blood-vessels and 

 secretes the horny substance. These closely- 

 packed whalebone plates, the number of 

 which may amount to 200 on each side, the 

 middle ones with a length of about 15 feet, 

 while the edge attached to the roof of the 



mouth is only about i foot in length, form 

 by their union an arched sieve, in the cavity 

 of which lies the tongue. The water runs 

 through the free fibres on the inner edges of 

 the whalebone, while all the small molluscs, 

 crabs, and fishes are retained. 



These enormous animals feed, in fact, 

 chiefly on small swimming creatures, shell-less 

 pteropods, crustaceans, &c., which swarm in 

 the northern seas, and are swallowed by them 

 in tons. The throat of the whalebone whales 

 is pretty narrow; but its narrowness has 

 sometimes been exaggerated, since fish of the 

 size of a herring can be swallowed quite easily. 

 It is known that the herring-fishers are very 

 glad to see the rorquals approach their coasts. 



