64 Part second. 



to side. (These movements are best seen, when a starfish' is lying on its 

 back and tries to turn over on its under surface. At the request of the 

 visitors the attendant will turn a starfish on its back.) The Brittle-stars 

 are able to perform snake-like movements with their long thin arms, and 

 some with branching arms swing them about like whips, and so progress. 

 The skin of the Sea-cucumbers is entirely leathery, and contains instead 

 of the calcareous plates innumerable extremely small pieces of carbonate 

 of lime, often of very curious shapes such as anchors and rosettes; they 

 are consequently able to straighten their body and bend it again in any 

 direction. In the Sea-urchins and Starfishes one can scarcely observe these 

 calcareous plates on account of the large number of spines and other 

 processes with which in life they are covered. But on dead specimens 

 the attendant has always some at hand one can easily see the im- 

 mense number of these plates : in large examples a hundred thousand 

 may be present ! 



How can Sea-urchins and Starfishes move about in the water ? In 

 answer to this question we must ask the reader to observe carefully 

 some specimen , which is attached to the glass front of the tank. He 

 will then notice on the side towards the glass numbers of fine threads 

 which bear at their extremities each a small sucker. These threads are 

 very mobile, stretch themselves and contract again like so many worms, 

 and are easily fixed to the glass. These sucker-feet are hollow, and 

 the animal forcing water into them causes them to elongate considerably; 

 when they have fixed themselves by their sucker they contract again and 

 draw the animal toward the point of attachment. The water necessary 

 for the expansion of the feet is taken into the body by a special system 

 of canals (which have nothing to do with the blood-system) leading to 

 every one of the feet. These feet are equally important to the Sea-urchins 

 to catch its prey. If any animal upon which they can feed comes into 

 their vicinity, they protrude some of these feet till they reach its body. 

 Should it not notice in time the attack which is being made upon it, it 

 is lost; other sucker-feet rapidly follow, and soon the prey is wound round 

 with hundreds of fine threads, and is slowly drawn to the mouth of the 

 Sea-urchin. All struggle is in vain, for if one or two sucker-feet are torn 

 away others take their place, and soon the prey gives up the fight and 

 is devoured. But, so as not to be recognized too soon in thus stalking 

 their prey, many Sea-urchins cover themselves on their upper surface with 

 ah 1 sorts of stones, shells, and pieces of sea-weed, and are thus more often 

 successful. The mouth of the Sea-urchins and Starfishes is on the lower 

 surface of the body, and is therefore only visible when they lie on their 

 back, or are attached to the glass on the front of the tank. May Sea- 

 urchins have five strong teeth of very complex structure ; others live 

 always buried in the sand and swallow it, so as to digest whatever or- 

 ganic substances it contains. The Starfishes have no teeth, but the walls 

 of their alimentary canal secrete such strong juices that they can kill 

 animals which they have caught with their sucker-feet and brought to their 

 mouth. Their food consists chiefly of shellfish, but often they will capture 

 fishes and crabs. They are one of the most formidable enemies of fishery, 

 especially of oyster-culture. 



