372 C. H. TURNER. 



those that with practice make rapid progress and fatigue rapidly, 

 those that with practice make slow progress and fatigue rapidly. 

 The average number of shocks required to induce a roach to make 

 ten successive refusals to enter the dark chamber was 51, the 

 least 16 and the greatest 118. "Marked individual differences 

 were noted with respect to the time during which the cock- 

 roaches retained their newly acquired habit. . . . No relation is 

 evident between the degree of permanency of the newly acquired 

 habit and the number of shocks necessary to establish it." He 

 gives learning curves, each of which he considers a special case 

 of Kraepelin's " Arbeitscurve." He found that animals with 

 amputated antennae can learn; but, in the case reported, it 

 required 126 shocks to induce it to make ten successive refusals 

 to enter the dark chamber. 



APPARATUS AND MATERIAL. 



The subjects of these experiments were the following types of 

 the common cockroach (Perlplaneta orientalis L.) : adult females, 

 adult males, larval females one half of an inch long, larval females 

 one fourth of an inch long, adult females with amputated 

 antennae. 



The following apparatus was used: an electric shocking plat- 

 form, electric batteries, an induction coil, an electrical switch key, 

 and discrimination boxes. Except for certain minor details of 

 construction, the electrical shocking platform is identical with 

 the one used by Szymanski. As used by me the platform con- 

 sisted of a thick block of wood 28.5 centimeters long and 23.5 

 centimeters wide, on the top of which two flat copper forks were 

 securely fastened with their tines interdigitating. Each fork 

 had sixteen tines. These tines were 19 centimeters long and 0.8 

 centimeter wide and each was separated from its neighbors, on 

 all sides, by a space about one millimeter wide. By means of a 

 binding post and wire the handle of each of these forks was 

 attached to one of the terminals of the induction coil, one to each 

 terminal. The induction coil had once been part of a medical 

 battery; the intensity of the shock was regulated by means of 

 a sliding core. Between the battery cells and the induction coil 

 there was a key for making and breaking the circuit. 



