RESEARCH SEMINAR. 325 



trical stimuli of from .6" to 2.0" according to the intensity of 

 the stimulus and the position of the organism ; (2) a shorter 

 reaction time when the radial canal regions are stimulated than 

 when the inter-radial regions receive the stimulus ; (3) rapid 

 fatigue with repetition of the stimulus ; (4) a reaction time to 

 photic stimuli of i" to 10" dependent upon conditions; (5) a 

 much quicker reaction to light when the organism is resting 

 subumbrellar surface uppermost (exposed to the light) than when 

 the exumbrellar surface receives the stimulus ; (6) a specialization 

 of organs for the reception of photic stimuli ; (7) the existence 

 of highly irritable and conductile tissues (nervous system) ; (8) 

 that excised organs rapidly lose their irritability ; (9) that varia- 

 bility of reaction time for comparative work should be expressed in 

 terms of percentage of the reaction time as well as in absolute terms. 

 This relative variability may be called the variation coefficient. 



August 2j. The Establishment of "Association by Con- 

 tiguity" in Hermit Crabs, Eupagurus longicarpus. By 

 E. G. SPAULDING. 



Crabs are naturally positively heliotropic. They were taught 

 to react against this by feeding them in a darkened portion of 

 aquarium. Coefficient of daily improvement in eight days = 

 6.00. The darkening screen was removed each time after feeding. 

 After seven days the crabs go behind the screen, when inserted, 

 although no food is there. This proves the existence (a) of asso- 

 ciation between two different stimuli and () that when one of these, 

 the screen, is presented, the usual effect of the other is internally 

 reproduced. This may be interpreted as conscious memory. 



August 24. The Resin Gnat and Three Parasites : A Study 



Made in July and August Under the Direction of Mr. Chas. 



T. Brues. By L. ECKEL. 



This study of Diplosis resinicola brought to notice three para- 

 sites, among a number of additional facts about this insect, whose 

 larval stage is well known to be passed within the lumps of resin 

 that exude from various species of pine, and which pupates within 

 the resin : 



i. Polygnotus pinicola, a proctotrupid which has been reported 

 as parasitic upon Diplosis pini-inopis. It destroys many of the 



