Hadley, Behavior of the American Lobster. 28 1 



in the following experiment. A large tube containing a number 

 of larvae was placed in an upright position on the laboratory table, 

 and the upper half covered with a roll of black paper. The larvae 

 gathered in the more brightly illumined end of the tube, which was 

 below. So long as they swam in the lower part of the illuminated 

 area, they assumed the normal swimming position, but whenever 

 they came into the upper regions, and approached the edge of the 

 black paper, the direction of the longitudinal body-axis was 

 changed from 30° below horizontal to 30° or even more above 

 the horizontal plane. 



Case 2j — In the following case the larva was oriented in the 

 normal swimming position and the screen was made to approach 

 from below. As a result the larva usually reacted by a slight for- 

 ward rotation, the head passing through an arc of a few degrees, 

 and producing a still greater angle between the longitudinal axis 

 and the horizontal plane. This new swimming position was sel- 

 dom subject to further modifications so long as the light conditions 

 remained unchanged. Regarding the reactions of the larvae of 

 Homarus vulgaris under similar experimental conditions, Bohn 

 (1905, p. 11) remarks: "Si la larve nage le dos dirige le haut, il 

 y a roulement de 90° ou de 180°, la par suite la larve devie laterale- 

 ment ou tombe." 



Such a result as the above was not observed by the writer. On 

 the other hand, it was observed that, whatever the body-orienta- 

 tion of a group of larvae might be previous to the approach of the 

 black screen from below, its presence usually determined a rise 

 of the larvae from the bottom of the container to the upper waters, 

 where normal swimming was manifested so long as the screen 

 beneath remained in place. When it was removed, however, or 

 replaced by a white screen, the consequent reaction was, as we have 

 already seen, characterized by rotations and revolutions through 

 90° or i8o°' These reactions in turn resulted in bringing the 

 larvae again toward the bottom, and in determining a consequent 

 absence of larvae in the regions near the surface of the water. 



Case 2^ — In this instance the larvae were oriented with back 

 below, and the black screen was made to approach from behind 

 in such a manner that the plane of the screen was parallel with a 

 vertical plane passing through both eyes of the larva. Under 

 these conditions (see Fig. 14, A') the reactions were as follows. 

 When the black screen. G. was introduced, the larva, A\ under- 



