260 THE OCEAN WORLD. 



complicated frame. They have a digestive and vascular system, and 

 a muscular system is almost always present ; in short, they have 

 internal or external respiratory organs, and a rudimentary nervous 

 system has been detected in many of the species. The nutritive 

 system is very simple, presenting in most of the family a single 

 orifice in the centre of the lower surface of the body, destitute of 

 teeth, performing the functions both of mouth and anus. De Blain- 

 ville says that " the liver is apparent and rather considerable in the 

 star-fishes, forming bunches occupying the whole circumference of the 

 stomach, and extending to the cavities of the appendages where these 

 exist." The mouth and gullet is admirably adapted for securing the 

 testaceous mollusks and other substances on which they feed. 



Reproduction in the Echinodermata appears to be monoecious. 

 Ovaries are, as far as is known, the only organs of generation. They 

 vary in number in different species. The sexes are usually separate : 

 the young are produced by eggs, the embryo of which undergo im- 

 portant metamorphoses. Immediately after birth, the young asterise 

 have a depressed and rounded body, with four club-shaped appendages 

 or arms at their anterior extremity. When they are a little more 

 developed, papillae may be observed on the upper surface, in fine 

 radiating rows : after twelve days the fine rays begin to increase, and 

 after eight days more two rows of feet, or tentacula, are developed 

 under each ray, which assist in the locomotion of the animal by 

 alternate elongation and contraction, performing also the office of 

 suckers. Like most other zoophytes, they have the power of repro- 

 ducing parts of their bodies which may have been accidentally 

 destroyed. 



ASTERIAS, on STAR-FISHES. 



As to the animal which commonly and sometimes scientifically bears 

 the name of Star-fish, in walking on the sea-shore at low tide, your 

 eyes have often seen this strange creature half buried in the sand. It 

 is so regular and geometrical in its form that it has more the 

 appearance of being the production of man's hand than of a creation 

 which breathes and moves. The Divine Geometrician who created it 

 never realised a -creature more regularly finished in shape, or more 

 perfectly harmonious in symmetry. 



