356 PKOCEEDINGS OF THE AMERICAN ACADEMY. 



nore the response, (2) recognize as many classes in the dark field as in 

 the light one, or (3) regard the response as equivalent to that of an 

 animal crossing the circle in the light field at an equal distance from 

 the directive axis. To ignore the response would obviously give un- 

 satisfactory results, for such animals certainly exhibit strong responses 

 either toward or from a given light. To create of them separate 

 classes would also be undesirable, for the records should express the 

 degree to which the worm turned from the normal, or, putting it the 

 other way about, how closely it came into orientation in line with 

 the axis of the lights. Since 90° (class 9) represents the extreme possi- 

 bility of turning from the normal axis, the creation of further classes for 

 crossings in the dark field would be misleading. The third possibility 

 is obviously the one to be adopted. Thus, if an animal turned so far 

 as to pass over the line at the point 13 on the side toward the small 

 light, the trial was recorded in class Sm 5. 



After the foregoing explanation the accompanying table (Table I) 

 will be easily understood. This gives the results of 100 trials made 

 with 10 individuals exposed to unilateral illumination, in this case to the 

 large light. The 19 vertical columns, numbered each way beginning 

 with and going to 9, correspond to the classes described above. The 

 individual numbered 3 (marked with an asterisk) is the same one that 

 is represented in Figure 5. In the columns next beyond columns 9 are 

 recorded the total number of crossings made on the Lg side of the 

 class and on the Sm side of that class, while in the columns next be- 

 yond these are indicated the number by which one of these exceeds 

 the other. From this it can be seen at a glance that when the worms 

 were headed away fi'om the observer (left side to light), they 

 crawled only 4 times toward the light (+ responses), 38 times aAvay 

 from the light (—responses), and 8 times straight ahead' (indifferent 

 responses). Thus there is an excess of 34 trials on the side of Sm. 

 The records for the worms headed in the opposite direction (right side 

 to light) are not so striking. These are: toward Lg, 17 ; toward 

 Sm, 26 ; indifferent, 7, giving an excess of only 9 toward Sm. Add- 

 ing these two sets together, we have : Lg{+), 21 ; Sm. (— ), 04 ; ( + ), 

 15 ; excess in favor of Sm, 43. Since 100 trials were made altogether, 

 43 per cent may be taken as an index of the negative response of 

 Allolohophora foetida to the large light alone under the conditions of 

 the experiments. 



The results of 100 trials under each of the three conditions, large 

 light only, small light only, and both lights simultaneously, are sum- 

 marized in Table II. The general arrangement of the data is similar 

 to that in Table I, except that the details of individual reactions 



