THE IMPENETRABLE SEA 



the penguin sometimes confuses the sexes of his own 

 species. Male and female are indeed difficult to dis- 

 tinguish, but one would imagine that the penguin him- 

 self would possess discrimination. Yet he will sometimes 

 take a pretty pebble to another male, mistaking him for 

 an eligible young lady. 



The jackass penguin is perhaps the most extraordinary 

 of them all. Darwin says that when crawling on ''all 

 fours" on the shore it possesses an agility of motion in 

 that attitude which is denied to all other penguins. It can 

 run on all-fours, even along the slope of a grassy cliff, and 

 at such a speed that it might well be mistaken for a quad- 

 ruped. This species derives its popular name from its 

 habit of throwing back its head and braying like a 

 donkey. 



Man's nearest competitors in underwater exploration, 

 the divers and penguins, can put up good performances 

 against his efforts as long as man uses no appliances. But 

 man is a tool-using animal, a fact that distinguishes him 

 from all others, and he has left his diving rivals far behind 

 by his invention of appliances during the centuries, par- 

 ticularly in the more recent developments of undersea 

 exploration. 



The Portuguese man-of-war and a few other creatures 

 have used their dependent tentacles or streamers as 

 ''sounding lines" for untold ages, but there has been no 

 development in them — they are appliances which can 

 only be used to "sound" any shallow shore areas in 

 which such creatures find themselves. The man-of-war's 

 tentacles cannot reach down beneath the surface beyond 

 a hundred feet at the extreme limit. 



Man's use of the sounding line — the third of his most 

 primitive devices for sea exploration : the other two being 

 the stone (held in his hands and later tied to his feet) 

 and the sponge — was very probably an extension of its 

 use for fishing. 



The history of soundings is lost in antiquity, even as the 



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