REACTION IN ASTERINA GIBBOSA. 429 



not observed in Asterina, and Jennings has seen it in Asterias 

 only when the tube-feet were prevented from taking hold. 



Method 6 is used by Asterina, but the turning is round an axis 

 transvei'se to the ray, not longitudinal as Jennings' account seems 

 to imply. (In general, the inverted Asterina tends to roll its rays 

 backwards from the tip rather than twist them to the side round 

 a longitudinal axis, as is customary in Asterias.) 



Method 1 is in Asterina as in Asterias the neatest and most 

 successful solution. Method 2 also occurs, but seems in Asterina 

 always to require the assistance of a third ray, which generally 

 supersedes one of the original pair. Method 4, as already pointed 

 out, is not mechanically possible in Asterina. 



It is in iVIethod 3 that the difterence between the two species 

 conies out most clearly. If Asterina tries to tvu-n on three rays 

 and the two outer get ahead, the middle one becomes sharply bent 

 back upon itself and is unable to straighten out owing to the rays 

 on either side pinning it down hard against the bottom. A dead- 

 lock follows, which lasts for several minutes, the two unattached 

 rays standing up a,lmost vertically in the water, the whole turning 

 movement being suspended half-way. 



One gets the impression that the starfisii is thoroughly puzzled 

 by the situation, an<l it certainly takes a long time to arrive at a 

 solution. Various solutions are found. In Case I. [su'pra, p. 425) 

 the starfish finally bent down one of the free rays and took hold, 

 then relaxed the tAvo outer attached I'ays enough to push the 

 middle ray through. In Case II. both of the free arms were bent 

 down and attached, then one of the original outer pair let go and 

 so released the prisoned ray. In Case III. the free arms bent 

 down and attached, pulling the body flat by main force, the 

 prisoned ray being subsequently freed by adjustment of tlie 

 neighbouring rays. In another case, not included in the general 

 series, in which the deadlock lasted about 4 minutes, an outer 

 ray let go, and the starfish turned on the other two attached rays, 

 the free arms taking no part in the solution. Case lY. in the 

 general series was of another character. Three rays had attached, 

 the tips of two rays twisting towards one another : then a fourth 

 ray took hold ; finally the starfish turned on a pair of rays at the 

 side, having taken over three and a half minutes to work out this 

 solution. 



In Asterias, when three rays attach and the outer rays get 

 ahead, as is apparently usually the case, tiuming is carried out 

 with comparative ease, the length and flexiljility of the rays 

 permitting the middle ray to crawl over or under the ones at the 

 side, instead of being pinned between them as happens in ^4s^erma 

 with its short and flat rays. 



I did not investigate the question as to whether the individual 

 Asterina shows any preference for using a particular i-ay or 

 combination of rays, as Jennings has demoiisti'ated for Asterias 

 forreri (1907, p. 144), but it is clear from the detailed records 

 given above that each individual tends to stereotype the method 



