2o8 'Journal of Comparative Neurology and Psychology. 



when the conditions previous to the hour of experimentation are 

 taken into account, it was found desirable to secure such condi- 

 tions for experiment that all influences which might be instru- 

 mental in determining the final reaction of the larvas either before 

 or during the time of actual experimentation should be clearly 

 recognized.. Accordingly, the data to be presented show not only 

 the nature of the reaction of the larval lobsters at a few chosen 

 periods in their life history, but they also make it possible to trace 

 modifications in reaction as the young animals pass on from stage 

 to stage and gradually approach the adult type. Numerical 

 results were usually obtained by counting the larvae which had 

 been imprisoned in difi^erent compartments of the box by the slid- 

 ing partitions. In other cases a large number of larvae were put 

 into a glass jar and the reaction of the majoVity was observed. 

 The separation and selection of larvae which gave either a positive 

 or a negative reaction to the same stimulus was thus possible, but 

 conclusions have been drawn only after a careful study of the 

 exact accounts of many groups of larvae. The exact intensity of 

 light used in the experiments was not known, but the experiments 

 were performed on such days and at such times as would make 

 the conditions uniform. Before entering upon a detailed con- 

 sideration of the experiments as a whole, it will be appropriate 

 to state some ground for assuming that lobster larvae react both to 

 the intensity and to the directive influence of light. The prelim- 

 inary experiments which led to this view may be presented as 

 follows : 



IV. PRELIMINARY EXPERIMENTS. 



Experiment I — Glass tubes 15 centimeters long and 2 centi- 

 meters in diameter were filled with salt water and in each were 

 placed six first-stage lobsters two days old. When the tubes were 

 held vertically, there was no tendency shown for the larvae to 

 gather in any particular region of the tubes. When, however, 

 a strip of black paper was wound in such a manner as to cover the 

 upper half of a tube (Fig. 2) and records were taken every minute, 

 the larvae became distributed as follows: 



