Marvels of the Universe 



213 



SATURN'S RING ABOVE THE CLOUDS. 



Saturn is hidden by clouds, but the Sun's light from below throws the planet's shadov 



of the planet's satellites is seen at the full. 



[Bij A . Twi'lle. 



the ring. Above, one 



SEA CUCUMBERS 



BY JOSEPH SINEI.. 



It is doubtful if any person outside the ranks of the zoologists would be able to trace any sign of 

 relationship between the leather-clad, sausage-shaped animals known as " Sea Cucumbers " and 

 the familiar Star-fishes and Sea Urchins of our shores. Yet the relationship is there, and they 

 are all included in the same division of the animal kingdom. 



Diverse as are these forms, they have more than one bond of unity. In their early stages they 

 are all alike, except in microscopic and technical details. They are at first little barrel-shaped 

 organisms that, except in a few cases, swim freely in the sea, and in these stages undergo many 

 wonderful transitions as they advance towards their ultimate and adult form. 



Even in adult hfe a common plan pervades them all. They are symmetrical and built on a 

 five-cornered plan. This plan, masked, varied, and in many cases aU but suppressed, can be traced 

 by close study. 



All, with the exception of the swimming form shown on page 214, have an arrangement of plates 

 or spines of lime either upon or within their skins. Even in their internal anatomy what at first 

 appears contradiction can be seen to be but variation. 



In the Sea Urchins the plates are jointed together to form the well known prickly 

 " shell." In the Sea Cucumbers the plates are separate and scattered within the substance 

 of the skin. 



As means of locomotion they possess a curious arrangement of what are termed " tube-feet." 

 These are simply tubes of thin elastic material, which can be protruded through holes in the skin 

 and into which water is forced by means of a series of canals termed the " water- vascular system." 

 These canals drawing in water from the sea through a portion of the skin specially modified to 

 act as a filter, forces it into the tubes and thus renders them turgid and enables them to act as 

 locomotive appendages. A little sucker at the tip of each tube allows of a hold upon the surface 

 travelled over, so that by this means the creature can progress at a fair rate. 



