Sensory reactions of Holothuria surinameusis. 253 



of application of the stimulus reacted more quickly than the posterior 

 ones, and the disturbance was generally carried farther in the 

 interior than in the posterior direction. By severe treatment, the 

 tube feet were caused to become retracted completely, as in 

 the third contraction stage described for the papillae (Fig. A, 4). 

 -Attached tube feet required much greater stimulation to induce their 

 contraction than did free ones. Tube feet were allowed to become 

 attached to glass rods, and were then gently pulled; this in most 

 •experiments led to contractions at the anterior and posterior ends 

 of the animal, and ultimately to the freeing of the tube foot, even 

 with very slight tensions. The tips of the papillae and the terminal 

 •discs of the pedicils were much more sensitive than their stalks. 



Stimuli applied to the lateral walls of papillae and pedicels 

 ,gave results which are of interest in view of von Uexküll's theory 

 of the action of the nerve net system in echinoderms. When the 

 side of a papilla not exactly perpendicular to the body surface, i. e. 

 in which the muscles were more contracted on one side than on the 

 other, was touched with a finely drawn out glass rod, or gently 

 pressed upon by a small bubble of air at the tip ol a pipette, the 

 Tesultant reaction involved two steps — (1) an erection of the 

 papilla, and (2) its collapse and contraction. This led to the reaction 

 -appearing as a positive one when the less contracted side was 

 touched, or a negative one when the more contracted side was 

 stimulated. The two steps were often fused together, but I believe 

 that we have here something parallel to the state of affairs at the 

 base of an Echinoid spine, where v. Uexküll (1900a) found the 

 stretched muscles to be more easily and quickly thrown into con- 

 traction. 



c) The body surface at the anterior and posterior extremi- 

 ties was much more sensitive than that in the mid-portion of the 

 animal's length. In the region within a centimeter or so of the 

 anterior end (varying with the size of the individual), a slight touch 

 on the dorsal or lateral surface between the papillae produced a 

 reaction from the tentacles, brim, aud nearby papillae, and some 

 longitudinal contraction of the body, together with more or less 

 turning to the side away from the point of application of the stimulus. 

 The mean of ten determinations gave an average reaction time of 

 0.4 sec. (at 26") for delicate tactile stimuli. The dorsal and lateral 

 surfaces in the middle region were relatively insensitive. To slight 

 touches no response whatever was secured, unless the particular area 



