94 



DIVERSIONS OF A NATURALIST 



The transparency and colourlessness of marine 

 animals which float near the surface is, on the other 

 hand, obviously useful, and to this group our jelly-fishes 

 belong. Not only do they escape observation by their 

 transparency and general absence of colour, but some 

 actually have a blue transparent colouring which blends 

 with the blue colour of the sea. Such are the gas- 

 holding, bladder-like sac as large as your fist called 

 the " Portuguese man-of-war," and the little sailing 

 Velella, both of which float, and even protrude above 

 the surface, so as to catch the wind. Others are only 



semi-transparent, and others 

 are marked with strong red, 

 brown, or yellow streaks. 

 Many of the smallest kinds 

 of jelly-fish have eyes which 

 are bright red in colour. 



The animals to which the 

 name " jelly-fishes " is now 

 more or less strictly applied 



FIG. 7. A common British 

 Jelly-fish. 



Aurelia aurita, usually as large are / as that fine ZOO logist 

 as a breakfast-plate and often . . . A . , N . , . . 



lar er Aristotle knew) in their struc- 



ture closely similar to the 



sea-anemones, but even simpler. They are called the 

 Medusse by naturalists. Their disk-like bodies are 

 largely formed by a jelly-like material, on the surface 

 of which are stretched delicate transparent skin, nerves, 

 and delicate muscles, whilst in the middle of the disk, 

 on the surface which faces downwards as the creature 

 floats, is the mouth, leading into a relatively small 

 pouched cavity excavated in the jelly, from which a 

 delicate system of canals is given off, and radiates in 

 the jelly of the disk. There is, as in the sea-anemones, 

 only one continuous cavity. The edge of the disk is 

 beset with fine, sensitive tentacles, sometimes many feet 



