II 



organs ; each arm on the underside is channelled along its centre 

 and contains a wonderful series of tube feet or suckers, supplied by 

 a system of water-vessels peculiar to star-fish and their allies. There 

 are hundreds of these suckers in each ray. These water-vessels are 

 supplied by a tube or calcareous filter which has its opening on the 

 upper side near the junction of two of the rays, and is called the 

 Madreporic tubercle, from some resemblance which the tube has to 

 Madrepore coral. The podia, or ambulacral feet, become erected by 

 being filled with water, and are then contracted, and by this opera- 

 tion movement is effected. But these creatures are also furnished 

 with organs of another sort which are still more wonderful ; they 

 occur very numerously among the sucker feet. These minute organs 

 were long regarded as parasites, but they are now known to be 

 pedicels specially modified to act as seizing organs ; they consist of 

 slender flexible stalks, the free end being divided into usually three 

 pieces, which are always opening and shutting and taking hold of 

 something ; it is supposed they act as cleansing organs by removing 

 particles of dirt, as well as temporary organs of fixation. At the tip 

 of each ray is a spot that is often spoken of as the eye, but the 

 animal has no true eye. Nevertheless, experiments have proved 

 that both star-fish and echinoids are sensitive to light and also to 

 smell. Star-fish live on dead fishes, oysters, and other molluscs, and 

 even on specimens of their own species. The organs for masticating 

 the food are highly developed and consist of a complex apparatus 

 known as the " Lantern of Aristotle." It is comprised of five sets of 

 pieces, and takes the form of an inverted pyramid ; the teeth are 

 very strong, and are capable of complicated and various movements. 

 I have said the star-fish lives on (among other things) oysters, 

 and its method of attack is a very curious and wonderful process ; 

 it has the power of extruding the stomach through the mouth, and 

 having surrounded the victim with its fine membrane, pours out its 

 gastric juice, which is a very penetrative solvent, and speedily kills 

 the oyster, which, having been reduced to a fluid condition (by the 

 action of the solvent), the whole is reabsorbed. A most interesting- 

 account of this operation is given by our friend Mr. Step in his 

 excellent little book " By the Deep Sea." 



All Echinoderms have the power of reproducing lost or injured 

 parts ; indeed, the star-fish from one arm can reproduce a complete 

 animal, and strange shapes often result in the course of regrowth. 

 All Echinoderms can right themselves if they are reversed, but the 

 methods are diverse ; the brittle star can easily perform the operation 

 by wriggling some of its arms under the inverted disc ; the common 

 star-fish has more difficulty, it twists round the tip of one or more 

 of its rays, and by the use of its sucker feet slowly drags itself over, 

 the whole operation lasting less than a minute. Brittle-stars : the 

 name Ophiuroidea given to these animals refers to their long serpent- 

 like arms, which are attached to a relatively small body, to which 

 they are appendages rather than portions of ; they have no groove on 



