W. J. CROZIER 629 



Strychnine. 



Chitons attached to the bottom of a glass dish were covered with 

 sea water, and later strychnine sulfate in sea water was added to the 

 desired concentration; or else the animals were immediately covered 

 with strychnine solution. The effects secured depended upon the 

 strychnine concentration and upon the time of action. 



In strychnine with a concentration of 1:10,000, after about 3 

 minutes (at 19°C.) the girdle of a Chiton begins to turn upward; the 

 foot ceases to attach to the substratum, and the whole body curls 

 upward at both ends; usually the animal falls over on one side, and 

 finally comes to lie more or less on its back because of lack of stable 

 support on the curved margin of the girdle; it later curls in the more 

 usual fashion, with the dorsal surface convex. Typical waves, fre- 

 quently several at a time, appear in rapid succession on the foot, 

 while the body is bent; and the proboscis is greatly extended. At 

 no time does the animal respond to a sudden shading of its dorsal 

 surface, although for a brief interval reactivity to a shading of the 

 ventral surface is greatly enhanced; shortly thereafter this kind of 

 irritability is obliterated. From this moment, that is after about 5 

 minutes exposure to strychnine, the Chiton responds to a sudden 

 increase of illumination upon its ventral surface by a very decided 

 further uncurling — whereas, in the non-strychninized animal, such 

 stimulation induces prompt curling. This reversal of the usual 

 reaction to increased illumination persists for about 15 minutes if the 

 Chiton is at this point returned to sea water; it is lost if the animal 

 continues in the strychnine solution for 24 hours, but even in this 

 case it reappears during subsequent destrychninization in sea w^ater. 



The initial phase of dorsalward (opisthotonic) curvature, due to 

 the contraction of the median longitudinal and oblique dorsal muscle 

 bands, is succeeded by the strong contraction of the ventral girdle 

 muscles and of the lateral longitudinal muscles, so that the body 

 becomes curled as in the usual curling up maneuver. The dorsal 

 shell plates are caused to separate slightly in tbi<s process, so that the 

 intertegmental mantle between each tv/o plates is exposed and open 

 to stimulation by touching it with a pointed instrument. In the 

 unstrychninized Chiton local stimulation of the mantle between two 



