h ' - ' 

 -7 



Vol. XVI. December, 1908. No. i 



BIOLOGICAL BULLETIN 



REGULATION OF' HARENACTIS ATTENUATA 

 IN ALTERED ENVIRONMENT. 



C. M. CHILD. 



In the course of several months work during the autumn and 

 winter of 1905-6 at the laboratory of the San Diego Marine 

 Biological Association, in La Jolla, California, I had the oppor- 

 tunity of investigating in some detail certain of the regulatory 

 phenomena and conditions determining them in Harenactis atten- 

 uata (Torrey, '02). Most of my work on this species was con- 

 cerned with restitution and will be presented elsewhere. Certain 

 of the data obtained, however, concern certain regulatory changes 

 which occur under altered external conditions. Since these are 

 of some interest in themselves and are not immediately related 

 to restitution, they are presented here, apart from the other data. 



I. THE USUAL FORM AND HABIT. 



Harenactis attennata is found in great abundance on the tide 

 flats of False Bay and San Diego Bay, living, as Torrey has 

 stated (Torrey, '02, p. 384), with the column imbedded in fine 

 sand, the axis of the body being perpendicular or nearly so to the 

 surface. When the animal is undisturbed the tentacles, twenty- 

 four in number, extend laterally over the surface of the sand, 

 though very often the tentacles appear as if in two sets, twelve of 

 them, alternating with the other twelve, extending more or less 

 upward and sometimes curved inward, while the other twelve ex- 

 tend laterally and may be curved slightly downward. Often, 

 when the body is well distended the column may protrude a short 

 distance from the sand. 



Any strong stimulus causes immediate withdrawal of the oral 



