SHALLOW-WATER STARFISHES 20I 



Between the extra bud and the normal one, on the other side, there 

 are six normal, equal rays, making fifteen normal rays, plus three 

 budding ones. 



This arrangement does not conform to any regular rule. The 

 extra bud is not due to replacement of a lost ray, for it originated 

 like the others. Before it apjjeared, this end of the body must have 

 had eight equal rays, which would have been abnormal, for five 

 would be the regular number. The interpolation of the new extra 

 bud may have been due to a tendency to resume an odd number of 

 rays at this end, which is the usual condition. The arrangement 

 may be formulated as follows, letting the figures represent normal 

 rays and the letters budding rays. If the extra bud (b) is simply 

 adventitious, the arrangement would be thus : 



234a56 78 



1 • 



234a56b78 



If the bud (b) be for regulation purposes it would stand thus : 



234a5678 



I 9. 



234a56b8 



In this case the bud would pair with ray 7. But this would give this 

 end of the starfish nine rays, instead of the normal number, five. 

 (See pi. Lxxv, figs. 3, 3a.) Probably autotomy would have taken 

 place later, followed by a regulation process by which the usual 

 number and arrangement of rays would have been resumed in one 

 or both parts. 



The budding in of rays in this species may continue till late in life. 

 A specimen studied by me, nine inches in diameter, having nineteen 

 fully developed rays, had a pair of small, equal budding rays in the 

 normal position, except that there were fourteen rays on the budded 

 side, instead of an odd number. There were five, as usual, on the 

 other side. 



A careful study of the living young of this species should be 

 made, where it is abundant, to ascertain more fully its complete 

 history during growth. 



In some cases the ambulacral plates are not strictly opposite, and 

 may even appear to be alternate, when the rays are strongly bent 

 sidewise, owing to their loose articulations. In a few cases the 

 number of these plates is not the same on the two sides of the groove, 

 for a short distance ; apparently due to the irregular interpolation of 

 an extra plate on one side only, here and there. When this occurs 



