472 



Variation in " Ophiocoma Nigra " 



•!•. As to the numher of rays. 



Forbes, in discussing the arrangement of the parts of Echinodernis* in general, 

 says : " The reigning number is five. The name of ' five-fingers,' eonimonly applied 

 by mariners to the star-fishes, is founded on a populär recognition of the number 

 reguant. It has long been noticed. Among the problems proposed by that 

 true-spirited but eccentric ])hilosopher, Sir Thomas Browne, is one, ' Why among 

 sea-stars, Nature chieHy delighteth in five points?' And in his Garden of C'i/rus 

 he observes: 'By the same number (five) doth Nature divide the circle of the 

 sea-star.'" Any deviation from this charactcristie number is, he continues, 

 "Always either in consequencc of the abortion of certain organs, or it is a 

 Variation by representation, that is to say, by the assumption of the regnant 

 number of another class " ; and " in ophiuroideaf the number five is absolute. 

 Colour and proportions are the subject of Variation." It is now well known, 

 however, that five is not by any means absolute, even as regards the Ophiuroidea, 

 for there are inany species whose rays habituaily number more than five. 

 Mr Bateson indicates the same thing in his .'ifatei-ials. Jeffrey Bell says*: "At 

 a very oarly stage in the evolution of the Echinoderma, the adult tended to acquire 

 a niarked radial symmetr}- ; but, at first, the number of niys was by no means 

 constantly five; now the symmetry is so geuerally c|uiniiuenulial that wonder is 

 nearly always expressed wheii the number five is diminished or increased." In my 

 investigations I found in the Hrst thousaud five specimens with six rays. (See 

 Table IV. and Fig 7.) In the second thousand I founri four specimens with six 



TABLE IV. 

 Showing Correlation of Parts of Six- Ray ed Specimens. 



* A Hislory of Britith Slar/i . Inii lii> lion, pp. xv., xvi. 

 t Op. eit., p. 20. 



X Cataloyue of British Echinodernis, Introductory Bemarks. 

 § Only four-rayed specimen found. 



