THE NATURALIST AT SEA. 3 



Many of these surface-floating forms are phosphorescent. 

 Such are best seen at night. Upon some evenings all the 

 water disturbed by the boat assumes the appearance of 

 liquid phosphorus. This phenomenon is due to the fact 

 that many of the minute organisms in the water are phos- 

 phorescent. The commonest light-emitting creature is a 

 tiny animal called Noctiluca. It is invisible to the naked 

 eye and is usually cherry-shaped. Sometimes, however, 

 its form is more like that of a kidney. From the depressed 

 side there projects a short whip-like process, termed the 

 flagellum, by the lashing of which the creature slowly 

 forces itself through the water. 



We now come to the Nekton, animals that are powerful 

 swimmers, such as fish, whales, sharks, dolphins, and 

 porpoises. Sharks abound in the tropical seas, as the 

 condition of some of the unfortunate " have-a-dive" boys 

 amply testifies. These evil fish, however, do not readily 

 show themselves, and the traveller cannot expect at the best 

 to see more than a dark fin. 



Whales, dolphins, and porpoises are mammals which 

 have taken to an aquatic life. A whale is no more a fish 

 than a dog is. It breathes by lungs, not by gills. The 

 female suckles her young. It possesses no fins, but swims 

 by means of its legs which have become modified into flap- 

 pers. Since lungs form the breathing organ of the whale, 

 it must continually come to the surface in order to breathe. 

 Then it is that the presence of the monster becomes known. 

 The " spouting " of whales is part of the breathing process. 

 When the whale wishes to take in a fresh supply of air he 

 comes to the surface, and just before he reaches it makes a 

 violent expiratory effort. Thus much air is forced out of 

 his nostril, which, passing through water, reaches the 

 atmosphere as a jet of spray. It is an error to imagine 

 that the whale ejects water from its nostril. 



Porpoises are common objects in the Indian Ocean. Like 

 whales, they are mammals. They are usually seen in 

 swarms or " schools," which often accompany ships for 



