250 ^- J- ÜEOZIEE, 



III. Mechanical stimulation. 



Echinoderms are known to be generally sensitive to a variety 

 of mechanical stimuli. The experiments of Eomanes (1885), Peeter 

 (1886), Jennings (1907), Cowles (1910), et al., have shown that 

 tactile and pressure stimuli play an important part in the behavior 

 of starfishes and ophiuroids. The apodous holothurians possess a 

 highly developed tactile sense (Claek, 1907, p. 47, 138). In addition 

 to touch papillae, synaptids have positional organs (Claek, 1901a, 

 1907, Bechee 1909), operating through mechanical stimulation after 

 the fashion of the molluscan and crustacean statocyst, which are 

 apparently irresponsive to vibrational stimuli. The tentacles and 

 podia ^) of pedate holothurians are usually spoken of as "tactile 

 organs", and the general surface of these animals is also sensitive 

 to pressure stimuli (Henei 1903a, b, c; Geave 1905; Peaese 1908). 



1. Local mechanical stimuli 



were applied to H. surinamensis by the use of needles, finely drawn 

 out glass rods, and minute bubbles of air formed at the tip of a 

 capillary pipette. 



a) The tentacles were very sensitive to slight touches. A very 

 slight stimulus led, in a resting animal, to the collapse of the ten- 

 tacle stimulated and its withdrawal; a more severe one, or a weak 

 stimulus repeated three or four times, produced complete retraction 

 of all the tentacles with or without an accompanying turning of 

 the anterior end to one side — the side away from that stimulated. 

 The reaction time was 0,3 sec.'-*), at 24 — 27^, and was (as nearly as 

 could be determined) constant for all intensities of stimulation, 

 though the amplitude of response varied in proportion to the severity 

 of the stimulus. The tentacles also responded in this way to fairly 

 strong water currents from a pipette. When all the tentacles had 

 contracted as the result of a stimulus applied to a single one, the 

 tentacle stimulated was the last one to reappear when the set was 

 re-extended. 



The tentacle reflex to mechanical stimuli affords a very clear 

 instance of the relation between a physiological state and reaction, 



1) As a matter of convenience, I shall use the term "podia" to 

 include merely the pedicels and papillae. 



2) All the measurements of reaction time recorded in this paper were 

 made with a calibrated stopwatch reading to 0,1 second. 



