252 W. J. Croziee, 



outline of a fully extended papilla; when gently touched, at x. the 

 thinner distal portion, yellow in color, collapsed through the with- 

 drawal of water into its ampulla and the contraction of its longi- 

 tudinal walls, and the outline seen in (2) was assumed; more vigo- 

 rously stimulated, the contraction proceeded to such an extent that 

 only a slight elevation remained upon the skin, (3); the final step, 

 involving the complete invagination of the papilla, could be secured 

 only on repeated stimulation; in this last stage (4) a small hole in 

 the integument was all that was seen from the outside. 



Mechanical stimuli of a more vigorous kind, such as gently 

 pinching with forceps, called forth reactions varying with the region 

 of the body concerned. On the most anterior part of the animal, 

 within a centimeter or so of the tentacle ring, pinching a papilla 

 led first of all to a contraction of the tentacles and collar, and of 

 the longitudinal muscles in such a fashion as to bend the anterior 

 end of the body away from the side stimulated, and then both the 

 affected papilla and its immediate neighbors would retract. If the 

 stimulated papilla was dorsal in position, the anterior end was bent 

 ventral and more or less beneath the body. To fairly severe stimuli 

 nearby papillae also reacted by slight contractions. The tentacular 

 brim was extremely sensitive to touch, its reactiveness being com- 

 parable to that of the tentacles. In the mid-body region, pinching 

 a papilla led to the contraction of nearby papillae also, especially 

 those on approximately the same transverse circumference. Further 

 evidence of the conduction of stimuli in circular fashion about the 

 mid-body was given by the transverse-muscle contraction, which 

 appeared as a narrow ring-like depression at the level of a vigo- 

 rously stimulated papilla; this type of response was usually not 

 accompanied by any sidewise turning of the anterior end. In the 

 region within a centimeter of the cloacal tip, pinching a papilla 

 produced a reaction of the posterior end comparable to that already 

 described for the anterior end, but less rapid and of not so great 

 an amplitude. The papillae forming a ring about the cloacal brim 

 were much more sensitive to tactile stimuli than the dorsal and 

 lateral podia; stimulation here effected a closure of the cloacal 

 aperture and more or less of a sidewise turning of the posterior 

 end of the body. 



The tube feet reacted to pinching by contraction, and neigh- 

 boring pedicels in an antero - posterior line running through the 

 stimulated pedicel also reacted; usually, those anterior to the point 



