56 



THE AMERICAN NATURALIST 



[Vol. XL 



At our request Professor Aschersohn of Berlin, had the kind- 

 ness to examine the species of plants found in the stomachs of 

 the dugongs, and determined the one to be Halophila ovalis (of 

 the Hydrocharidacefe) and the other a species of Zostera (Zos- 

 tera capricorni Aschersohn). The latter grows as a dense or 

 scattered low bed, while in Halophila the root stalk and petiole 

 are hidden in the sand and only the small leaflets project slightly. 

 These two plants do not occur on rocky bottoms. The Halophila 

 growth is limited to a depth of about six meters below the low 

 tide mark; higher up, the growth becomes sparser until it entirely 

 disappears. The white sand, peculiarly flecked and spotted by 

 the Halophila leaves, is the especial feeding place of the dugong. 

 The slight depths at which the dugong's food plants can grow 

 also explain why the animal spends part of its life in the shallow 

 seas and part in the off-shore waters. 



Among the beds of Halophila are the so called dugong's tracks 

 which at once show us how the animal takes its food. The tracks 

 are long, curved, or wavy furrows in the white sand, with sides 

 parallel, about four fingers broad and from four to six cm. deep. 

 They are completely denuded of the Halophila. Their age is 

 determined by the condition of their edges; fresh tracks have 

 raised, sharply defined edges rising from one to two cm. above 

 the sea bottom. If the strong flood tide has swept over them 

 once, the sand becomes washed away, the edges obliterated, and 

 the depth less, until finally they are entirely washed away. These 

 furrows, showing white through the dark water, indicate the 

 presence of the dugong. They are produced by the dugong pass- 

 ing over the Halophila beds as it feeds, pulling up the plants 

 with its palatal processes, seizing them and perhaps washing 

 them free of sand and other extraneous matter after the manner 

 of certain waterfowl (ducks), and then chewing them up with its 

 molar teeth. The dugong trails are not made up of separate 

 marks which would indicate that the food is not plucked or bitten 

 off in tufts. Such plainly continuous trails could not be made 

 by the animal's lying sluggishly at the sea bottom. Also the 

 peculiar lateral mark made by the tusks^ in case of the male is 



1 Finsch believes that the tusks serve for uprooting the sea grasses rather 

 than as weapons, but the fact that they are lacking in the females, argues 

 against this view. 



