256 'Journal of Comparative Neurology and Psychology. 



having been placed in the dish), the lobsters began to plough 

 through the sand of the bottom, especially near the rim of the con- 

 tainer, and to construct burrows beneath shells, stones or other 

 objects in the sand. Yet, even after these burrows were com- 

 pleted, the fourth-stage lobsters seldom remained in them, but 

 came out and crawled rapidly over the bottom or swam more or 

 less actively near the surface of the water. When, on the other 

 hand, fifth-stage lobsters were introduced into the dishes contain- 

 mg sand, gravel, and shells they commenced burrowing at once 

 and when the burrows were completed they showed a much greater 

 tendency to remain therein than did the late fourth-stage larvae. 

 Although the fifth-stage lobsters came out for food, free swimming 

 was seldom indulged in during such sorties. The question now arises 

 as to what conditions or factors cause the energetic surface-swim- 

 ming of the early fourth-stage lobsters and the bottom-seeking 

 and burrowing habit of the late fourth and the fifth stage. Are 

 these reactions to be explained as phototropic, geotropic, or thig- 

 motropic reactions .^ Or do all three of these, and perhaps still 

 other factors, unite in determining the final result ? While we 

 are not yet prepared to venture an answer to these queries, the 

 records of a few simple experiments which were undertaken to 

 ascertain the value of the part played by contact-irritability in 

 determining the orientation of the fourth and fifth stage lobsters, 

 under certain known conditions, will be presented. 



Experiment 2g. Fourth-stage lobsters — The technique em- 

 ployed in the present experiment was as follows: One-half of the 

 bottom of box By was sprinkled with sand to the depth of five 

 mm., the box was filled with salt water to a depth of 3 cm., ten 

 early fourth-stage lobsters were introduced, and the box covered. 

 The aim was to learn whether, in the total absence of light, the 

 larv^ would "choose" either the sanded or the clear area. The 

 result of a typical test is presented below. The readings were 

 taken every five minutes, and after each reading the lobsters were 

 caused to distribute themselves about the box: 



Sanded area. 



Clear area. 



