430 MR. E. S. RUSSELL ON THE RIGHTING 



used in the first few trials. Some specimens, notably B and G, 

 tvirned unhesitatingly on an adjacent pair, F showed a tendency 

 to attach all its rays, H got itself tied np in a deadlock three 

 times in ten trials, K showed a pi'opensity to use one ray for 

 turning. It is difficult to say whether these tendencies are due 

 to individual idiosyncrasy or to the foi'mation of transitory habits. 



Perceptions involved in the Righting Beaction. — When Asterina 

 is turned on its back two obvious changes take place in its 

 relation to environment — the tube-feet lose contact Avith the 

 bottom, and the action of gravity upon the animal is reversed in 

 direction. The irritating effect of light upon the ventral surface 

 need not be considered as an essential factor, for, according to 

 Preyer (1886-7, p. 99), the righting reaction may take place in 

 the dark. The stimulation of the dorsal surface by contact with 

 the bottom may also be eliminated from the essential conditions, 

 since Asterina is often found under stones with its back in contact 

 witli the bottom. And Preyer {ibid. p. 107) has shown that 

 removal of large pieces of the dorsal integument does not hinder 

 the righting reaction. 



In order to study the relative importance of the two main 

 conditioning factors — contact and gravity — I carried out the 

 following experiments on the beach with a, couple of large and 

 active specimens : — 



I. The starfish was turned on its back, and a small piece of 

 slate was held 1-2 mm. above the ventral surface. The starfish 

 attached completely and coidd be lifted away adhering to the 

 slate — the righting reaction was not carried out, the starfish 

 remaining back downwards. If, however, the slate was not lifted 

 away and the starfish remained in contact with the bottom, it 

 left the slate and crawled on to the bottom, thus completing the 

 righting reaction, (10 trials.) 



II. The slate was presented half-way through the turning 

 movement. The starfish attached some of its tube-feet tem- 

 porarily but completed the turn towards the bottom. (10 trials.) 



III. A piece of Fiicus of about the same area as the starfish 

 was placed on the ventral surface of an inverted Asterina. The 

 animal attached its tube-feet and carried out "walking" move- 

 ments witli them, by means of Avhich the weed was carried right 

 ofi' the ventral siu'face. The starfish then proceeded to turn. 



IV. The starfish was held lightly in position by means of 

 angled pins on the under side of a floating block of wood, the 

 ventral surface facing earthwards. It turned so as to bring its 

 ventral surface into contact with the wood. In spite of the fact 

 that the pins inlerfei'ed somewhat with the righting movements, 

 less than one minute suifieed in two cases for the turn, less than 

 two minutes in three other cases. 



V. Propped up with its back against a vertical side of rock, 

 the starfish invariably turned towards the eai'th, pivoting rapidly 

 on the pair of arms whose tips were in contact with the horizontal 

 surface. 



