35() J. M. D. OLMSTED 



f 



former position on the plate, thus avoiding a displacement of 

 the body by gravity which would have influenced its orientation 

 when it fell. In every case the head end turned and bent up- 

 wards at right angles to the rest of the body, and then, as its 

 tentacles pulled the Synaptula upwards, after orientation had 

 been perfectly accomplished, the body finally fell so that the 

 animal lay in a straight line throughout its entire length. 



These results tend to show that the head region is concerned 

 In orientation to gravity. For further proof the 'heads' of 

 specimens were cut off immediately back of the calcareous ring. 

 Both these 'heads' and the decapitated bodies were used in 

 experiments. In every instance the head portions climbed the 

 vertical walls of the vessel, while the posterior portions remained 

 on the bottom in an inert condition. Naturally one can not 

 conclude from such experiments that the posterior ends are 

 unable to orient to gravity, since as a matter of fact they were 

 deprived of their organs of locomotion, the tentacles, and 

 therefore might not be able to show any response. To see 

 whether lack of locomotor organs prevented response, I took 

 whole specimens, anaesthetized them in chloretone, and cut 

 off their tentacles. When on the next day they had recovered 

 from anaesthesia, I placed these tentacle-less specimens together 

 with 'headless' ones, anterior ends downward, upon a plate 

 covered with cloth. Although neither the tentacle-less nor 

 the headless animals could climb, they were able to cling to the 

 cloth by means of their anchors. When the plate was inclined 

 at an angle of 30 with the horizon, the extreme anterior 

 ends of the tentacle-less specimens bent around so that their 

 bodies were in the form of a J, while the headless ones remained 

 as they were placed, or at most became slightly bowed. The 

 organs concerned with orientation to gravity therefore can lie 

 only in the anterior end of the animal near the calcareous ring. 



To show that this was a true response to gravity, and not 

 to the need of oxygen, I placed several 'heads' in a finger-bowl 

 completely filled with sea-water and inverted in a second dish 

 of sea-water. The rim of the finger-bowl was slightly raised 

 so that the supply of oxygenated water might enter from below. 



