428 Jill. E. S. IIUSSELL ON THE RIGHTING 



used by Asterias forreri shows that Asterina attempts practically 

 all the methods employed by Asterias, but is successful only in 

 the n>easui'e that its organisation permits. Asterina is a short- 

 rayed, compai'atively rigid form, and cannot twist its rays (espe- 

 cially round a longitudinal axis) to anything like the extent 

 possible to the long-rayed Asterias. Its righting reaction is 

 accordingly less vai'ied than in Asterias, for the simple reason that 

 certain solutions open to Asterias are mechanically extremely 

 difficult or quite impossible for Asterina. Organisation, in fact, 

 must be regarded not only as a means towards action, but also 

 as a limit upon activity — a limit which the animal in its active 

 striving tries always to overcome. 



The following is a summaiy in Jennings' own words of the 

 various njodes of righting which he has observed in Asterias 

 forreri : — 



" 1. The simplest and neatest method of turning is the follow- 

 ing : Two adjacent rays twist their tips in such a way that the 

 ventral surfaces of the two face each other ; then the tube-feet of 

 these rays attach themselves and throw the starfish over in a neat 

 somersault 



"2. The tips of the two adjacent I'ays may so twist that the 

 vential surfaces do not face each othei-, l)ut both face in the same 

 direction. The tube-feet then take hold and throw the starfish 

 over, — twisting it about an axis which passes lengthwise through 

 one of the attached rays. This method of turning is extremely 

 difficult and awkward, biit is seen at times. Usually when two 

 rays become attached in the way described, a third ray takes hold 

 and aids the turning, the method then forming a transition to 

 that given next 



" 3. Three adjacent rays twist, attach themselves, and remain 

 attached, all pulling throughout the reaction. Usually the animal 

 turns primarily by the aid of the two outer rays, while the 

 middle one is relatively passive, and is compelled to double back 

 under as the animal turns. Often this middle ray walks back- 

 ward beneath one of the othei' rays, or the other walks actively 

 over its surface or there is a combination of these two movements, 

 till the normal position is reached 



" 4. Four of the I'ays take hold, two extending to the right, 

 two to the left [all remain attached during the turn]. 



" 5. All of the rays attach themselves. Now the turning can 

 be accomplished onl}^ by the release of certain lays 



" 6. An unusua,l method is that in which but one ray twists 

 and attaches itself, and by its unaided efiorts turns the starfish 

 about an axis passing through this ray 



" 7. A still more unusual type is seen in the performance of 

 the righting reaction without attachment of the tube-feet of any 

 of the rays ...."( 1 907, pp. 1 25 & 1 28). 



This last method, in which the starfish raises its disc high by 

 standing on the tips of all five rays and then swings one or more 

 rays over or under until it topples over right side up, I have 



