74 THE WONDER OF LIFE 



water is a pronounced indigo colour. From the equator 

 to beyond the thirtieth parallel, the colour of the surface 

 water is a pure and brilliant ultramarine. The ohve- 

 green, the indigo and the ultramarine are the three great 

 colour-types of the sea. 



Open Sea. — One must be careful to notice that pelagic 

 does not mean at the surface ; it means ' open sea ' and 

 as far down as clear light reaches. Many small organisms 

 have their maximum at a depth of 50 fathoms below the 

 surface, and a great advantage of being several fathoms 

 down is that a measure of calm is enjoyed. Dr. A. G. 

 Mayer brings this out very vividly in his memoir on the 

 Ctenophores or ' sea-gooseberries ' of the Atlantic coasts 

 of North America — fascinatingly beautiful animals of 

 the CcBlenterate series, distantly related to Medusoids. 



' In the extreme tenuity of their bodily substance and 

 their diaphanous delicacy of coloration, the ctenophores 

 stand apart from other marine animals. Their presence 

 in the water is commonly denoted only by the brilliant 

 flash of rainbow colours, which play along the lines of 

 their ciliary combs as they move languidly beneath the 

 unrippled surface of the sea. Yet these creatures are 

 no more wonderful in their complex organization than 

 in their remarkable adjustment to their habitat : for so 

 delicate are most of them that a current such as that of 

 an oar suffices to tear them into misshapen shreds — a fate 

 which they escape in time of storm by sinking far into 

 the depths. This fact accoimts for the extreme rarity 

 of many of these forms, for the ocean's surface must have 

 remained flat as a mirror for many hours before they can 

 be lured upward from the calm of their deep retreat.' 



We must distinguish between the surface plankton 



