SURFACE-SWIMMING FAUNA (INVERTEBRATES). 115 



Arctic Star-fishes the larval life is in a similar 

 manner abbreviated and protected, and it seems 

 probable that this may be accounted for by the 

 fact that the surface waters, where the larval 

 forms would live if they were liberated, are for 

 very long periods covered with ice. 



The great group of the Crustaceans also presents 

 us with many interesting larval forms specially 

 adapted to surface life. In a previous chapter 

 I have pointed out that the Barnacles of our 

 coast give birth to curious little free-swimming, 

 six-legged larvae called Nauplii, which after hav- 

 ing undergone two or three further changes, 

 settle down on a rock and assume the adult 

 features (see Fig. 12). 



It is not known how long these changes take 

 in the ordinary course of nature, but it is quite 

 probable that the larval life is a comparatively 

 short one. 



Some Barnacles, however, live far out at sea 

 on drifting wood or parasitic on the skin of 

 Whales, and it is reasonable to suppose that 

 when their larvae are hatched a very consider- 

 able time may elapse before they find a suit- 

 able resting-place to complete their metamor- 

 phosis. 



The life-histories of these species are not at 

 present accurately known, but a few remarkable 

 Nauplii have been found which, there is reason 

 to believe, are really the Nauplii of some kind 

 of Barnacle and are specially adapted to a long 

 life at the surface by the enormous length of 

 their spines. 



In the specimen discovered by Chun in the 



