COMPLEX KESPONSES 155 



supplied with running seawater that had been artificially 

 cooled to about 8 degrees centigrade, they remained fully 

 expanded in the dark and would shorten in the light. 

 They responded to a mechanical stimulus by contraction, 

 and in other respects they reacted as they did under more 

 usual temperatures. 



If sea-anemones in seawater at 23 degrees centigrade 

 are flooded with water at 35 degrees centigrade, 

 even though they are kept in the dark, they invariably 

 contract completely. This response is in general agree- 

 ment with what was found by Fleure and Walton (1907), 

 namely that Actinia and Antliea retract at temperatures 

 above 22 degrees centigrade. If, however, Metridium is 

 subjected to a gradual change of temperature which 

 eventually reaches 36 degrees centigrade, it slowly loses 

 its responsiveness to mechanical and chemical stimuli and 

 soon dies. The loss of responsiveness begins at about 34 

 degrees centigrade, and is complete at 36 degrees centi- 

 grade. An animal kept a few minutes in seawater at 35 

 degrees centigrade may be touched repeatedly on the col- 

 umn near the pedal disc without showing any response 

 and may be eventually killed in alcohol in an expanded 

 condition. Animals which have thus been rendered in- 

 sensitive seldom recover, but in the course of a day or 

 so die. 



So far as Metridium is concerned, subnormal temper- 

 atures have little influence on its responsiveness except 

 possibly on the rate. Supernormal temperatures, if 

 quickly applied, induce general contraction; if gradually 

 applied and of sufficient intensity (35 degrees centigrade), 

 they bring about a condition of non-responsiveness that 

 quickly passes over without contraction into one of death. 

 Whether the tentacles are receptors for temperature 



