RADIATA. 3*0' 



the animal has the power of locomotion, sometimes by means of the 

 arms, and sometimes with the aid of tlie sucker-like feet. The arms in 

 some genera are provided with numerous lateral filaments, and in some 

 cases they, divide into branches. The genus Astr^ophyton (named also 

 Eiiryale and Gorgonocejyhalus) (jyl. Tf5, ß(j. G3), is remarkable for its 

 five dichotomizing arms sending off branches, and terminating in a nmlti- 

 tude of curled filaments, which, it is said, may amount to eight thousand in 

 a single individual. 



The genus Ophiura {pi. 76, ßg. 64) is named from the resemblance 

 which its long and slender arms bear to the tail of a serpent, not only in 

 form, but in the numerous bony pieces of which they are composed, 

 and which are not unlike the scales of a serpent. The arms are very 

 flexible; and by giving them an undulating motion, the animal caji 

 swim to a certain degree. On each side of the base of the arms is an 

 opening which is the outlet of the ovaries, of which there are ten. Several 

 species inhabit the coast of the United States. In Ophiolepis {fig. 62), a 

 genus allied to Ophiura, the disk is entire, with smooth plates. In both 

 genera the arms have movable spines, which in some species are appressed, 

 and in others projecting. The species figured, 0. scolopendrina^ is found 

 near the Isle of France. In these genera the mouth is in the centre of the 

 ventral surface, and from it are continued five grooves, through which a 

 few sucker-like feet are projected. The mouth is armed with a strong 

 osseous apparatus for masticating food. The arms, when broken ofi*, can 

 be reproduced. PI. 1Q.,fig. 61, represents Astrogonium granuläre of the 

 seas of northern Europe. Li this genus the rays are not so well developed 

 as in Asterias {fig. 60), which gives it a pentagonal figure. 



Greasier turrifns (pi. 76, fig. 59) attains a length of ten inches, and 

 inhabits the Indian Ocean. 



Solaster is distinguished by an increased number of rays ; S. papposus 

 {pi. 76., fig. 66) is a foot in diameter. 



Stellonia rithens {fig. 65) attains a foot in size, and is so abundant in the 

 seas of Europe as to be spread over the soil as a manure. 



Asterias {fig. 60) has the rays so much enlarged that there is room in 

 the concavity of each for two extensions or appendages of the stomach, 

 with an ovary between them, and a liver; which is not the case in the 

 slender rayed genera like Ophiurvs. Moreover, the size of the rays renders 

 them less flexible, and badly fitted for locomotion ; but as a compensation, 

 they are pierced along their inferior surface (between short transverse, bones 

 arranged in series on each side of a deep central groove) with a multitude 

 of ambulacral perforations, through which the feet already mentioned project, 

 and which enable the animal to crawl up a surface as smooth as glass, and 

 also assist in holding: its prey. The sucker-like feet are connected 



ö 



within the aperture through which they project, with a globular vesich^ 

 filled with water, by the hydrostatic action of which the suckers are extended 

 or withdrawn. Each vesicle is connected by a small tube with a canal 

 which traverses each ray, starting from a circular canal around the 

 oesophagus. 



243 



