412 INTEODUCTIOISI TO ZOOLOGY. 



sive activity and playfulness of its gambols, and the evident 

 predilection which it evinces for society, are recorded by every 

 mariner ; numerous herds of them will follow and surround a 

 ship in full sail, with the most eager dehght throwing them- 

 selves into every possible attitude, and tossing and leaping 

 about with elegant and powerful agility, for no other apparent 

 reason than mere pastime."* 



The common Porpoise {Plioccena communis, Fig. 323) is 



Fig. 323.— Porpoise. 



scarcely less playful or less sociable. It is the most common 

 species of Cetacea around our coasts, entering our bays in 

 pursuit of shoals of herrings and other fish, and attracting 

 attention by the manner in which it rolls over, as it comes to 

 the sm-face to breathe. A herd of them may be sometimes 

 seen, indulging in their unwieldy gambols, and chasing each 

 other in sport. " On the approach of a storm, or even in the 

 midst of the tempest, they appear to revel in the waves, 

 showing their black backs above the surface, and often throwing 

 themselves wholly out of the water in their vigorous leaps." 

 The length of the body is from four to six feet. 



To the same group belongs the Bottle-head Whale {Hy- 

 peroodon), occasionally taken on our shores ; the Round-headed 

 Porpoise or Caaing Whale {Phoccena melas), which appears 

 in herds of several hundreds ; and the Nainvhal (Monodon 

 monoceroi), whose single projecting tooth, six feet or more 

 in length, has procured for it the name of Sea-Unicorn. 



Physeteridoe. — " The common Cachalot, or Spermaceti 

 Whale, is well known," says Professor Bell, "as affording 

 that peculiar and useful substance from which it takes its 

 common name. The enormous size of the head, in length 

 very nearly equalling, and in its bulk even surpassing, half of 



* Professor Bell's History of British Quadnipeds. From this work we have 

 enriched our brief notice of the Cetacea with several extracts. 



