GENERAL HABITS AND INSTINCTS. 485 



siderable quantities, tlie purpose of which habit is still a matter 

 of coDJecture. Sailors, and even some intelligent naturalists, 

 believe they serve as ballast, and some affirm that a larger quan- 

 tity is swallowed when the animals are fat than when they are 

 lean, and that when they are very fat thej^ require them to give 

 their bodies the proper specific gravity to enable them to remain 

 easily under water. Whatever may be the cause, the strange 

 fact rests on abundant and trustworthy evidence. Most species 

 of Seals are strongly attracted by musical sounds, but whether 

 their interest is merely that of curiosity or real fondness for such 

 sounds may be fairly judged to be an open question. That they 

 possess a great deal of curiosity admits of no doubt. 



One of their most remarkable traits is the great length of 

 time they are able to remain under water. Mr. E. Brown 

 states that the average time is five to eight minutes, and that 

 he never saw them remain below the surface for more than fif- 

 teen minutes, but other observers give from twenty minutes to 

 half an hour. Various theories have been offered in explana- 

 tion of this remarkable power in a warm-blooded, air-breathing 

 animal, but none seems satisfactory. It has by some been sup- 

 posed to be due to the large size of the venous system of circu- 

 lation; by others to venous sinuses in the liver and surrounding 

 parts, which serve as reservoirs for the venous blood ; by others 

 to the large size of the foramen ovale; while still others deem 

 it to be wholly physiological and not structural. Some of 

 the Arctic species have the habit of forming breathing-holes 

 through the ice, through which they not only rise to breathe, 

 but ascend to bask on the ice. These are circular, with smooth 

 sides, and are kept open by constant use, and are believed to 

 be made while the ice is forming. Other species keep near nat- 

 ural openings formed by the winds and currents and never con- 

 struct breathing-holes. 



Strange as it may seem, it is a well-established fact that the 

 young Seals take to the water reluctantly and have to be act- 

 ually taught to swim by their parents. Th& young of some 

 species remain entirely on the ice for the first two or three 

 weeks of their lives, or until they have shed their first or soft 

 woolly coat of hair. Those that are brought forth on land, as 

 in the case of the Elephant Seals, are, like the Otaries, timid 

 of the water, swim at first awkwardly, and tire easily in their 

 first efforts. 



Seals utter a variety of cries, from which they have derived 



