168 THE OCEAN 



a series of blue-coloured animals, like Porpita^ 

 Velella, Physalia and lanthina, which viewed 

 from below must be nearly invisible, hence 

 protected from enemies. 



Immediately below the surface most animals 

 are transparent and colourless, like the leptoce- 

 phalids and many other larvae, which when 

 taken from the tow-nets are often distinguish- 

 able only by their little black eyes, their blood 

 being devoid of haemoglobin and the entire 

 body perfectly transparent. Others are sil- 

 very, with a bluish back, like the herrings and 

 flying fishes. Animals living in the vicinity 

 of floating objects, such as logs of wood or 

 clusters of gulf weed, exhibit a marvellous 

 resemblance in colouring to the objects they 

 accompany : as typical examples of such pro- 

 tective colouring we may cite the little crab 

 {Planes minutus) and the little fish (Anten- 

 narius marmoratus) associated with the float- 

 ing gulf-weed of the Sargasso Sea. 



In depths of 100 or 200 fathoms the fishes 

 are usually laterally compressed, grey in 

 colour or with silvery sheen, often iridescent, 

 on the sides, and blue-black or brown on the 

 back. This arrangement seems admirably 

 adapted for rendering the animals invisible 

 when viewed either from above or from 

 below — ^the fish Argyropelecus is a good 

 example. 



