No. 577] 



NUMBER OF BAYS IN ASTEBIAS 



Martens (1866, quoted by King, 1898) for this species. 

 I have not been able to substantiate this idea by laboratory 

 experiments, for, in my tests, single isolated rays did not 

 live more than a few weeks. 



(b) Newly forming rays have a tendency to appear in 

 symmetrically disposed pairs (see Fig. 12), which gives to 

 r, n u i fat fig. i2. 



many individuals a strikingly bilateral aspect. This is 

 accentuated by their behavior, for, in the absence of 

 directive stimuli, they commonly move with the longest 

 rays in advance. In moving away from the light, the loco- 

 motor movement of the group of longer rays also tends, 

 in many cases, to produce a spurious " orientation. " 

 When placed oral side up, the larger rays exert a de- 

 termining influence on the direction and manner of right- 

 ing. These effects are due to the greater pedicel and 

 muscle development of the longer, thicker, rays. 



The formation of two rays at a radial cut on the disc 

 was found by King (1900) in Asterias vulgaris. 



V. I have suggested, above, that Asterias with 7 sub- 

 equal rays have probably arrived at that condition by 

 different routes. One method of ray multiplication ap- 

 pears to be the spontaneous addition of new rays at any 

 point on the disc. Twelve starfish were found which 

 showed but one ray markedly shorter than the others. 



