332 EDWARD C. DAY 



Table 3 gives the results of this test. Stimulation was made 

 with a beam 5 mm. in cross-section. The pencil of light was 

 small enough to afford a more restricted localization of the 

 stimulus both on the siphons and over the gangUonic area. 

 Under these conditions the ganglion again exhibited its decided 

 sensitivity to light in comparison with the insensitiveness of the 

 siphons, yielding 26 responses out of 33 trials to only one 

 response for the incurrent and none for the excurrent out of 35 

 trials apiece. 



From the summarized table it will be noted that when the 

 ganglionic region was stimulated the animal gave 58 responses 

 (closure of siphons) out of 65 trials, while to stimulations of the 

 other regions, the incurrent siphon yielded 6 out of 70, the ex- 

 current 3 out of 41, and the body 1 response out of 35 trails. 

 It was the larger of the two beams of light which was effective 

 in eliciting responses when siphons or body were stimulated. It 

 will also be observed that the latent period of response was longer 

 for the smaller beam (8.9 seconds) than for the larger one 

 (4.2 seconds) ; i.e., the larger the area stimulated, the shorter is 

 the reaction time. 



WTien the body region was illuminated with a beam about 4 

 cm. in diameter, it squirmed and contracted in that region, 

 while both siphons remained open. Only two of the five Cionae 

 responded in this manner, however. The reaction time in the 

 one case was 18 seconds and in the other 26 seconds. Although 

 the animals lay submerged in a depth of 4| cm. of sea-water, 

 this comparatively slow reaction time may have been due to the 

 thermal effect rather than to the actinic effect. A thermometer 

 placed at that depth and illuminated for twenty seconds showed 

 a rise of temperature of 0.2°C., but no experiment was performed 

 to decide the point in question. 



