NATURAIy HISTORY OF AMERICAN I^OBSTER. 355 



contact with solid bodies, began to assert itself and thus to modify the previous sensi- 

 tiveness to Ught, apparently leadinp^ the animal to crawl under shelter and to burrow 

 in the sand or mud at the bottom . 



Previous to the fifth stage an increased intensity of light in certain cases may 

 reverse the response, while in others it does not. After the fifth stage no reversal of 

 the response can be effected in this way. 



We will now review some of the observations of Bohn on the movements of the 

 larvae of Homarus gammarus of Europe, reported in 1905. He beheved that t he newly 

 hatched young were immediately attracted to the surface, since they are positively 

 phototactic . At first they approached the fight, while later, at the end of some days, 

 they moved toward regions of greater obscurity. Upon the swimming movements and 

 unstable equilibrium of these larvae this observer remarks as follows : The back of the 

 lobster does not remain constantly directed upward, but is alternately incHned to the 

 right and left, sometimes as much as 90° It can fikewise tip over by turning on the 

 long axis of its body. The displacement of the body is effected not by the position of 

 the longitudinal axis alone, but by that of the vertical axis of the cephalothorax as well. 

 If the carapace is elevated, the animal both advances and rises; if it is incHned to 

 the right, the larva advances by deviating to the right, and the more considerable the 

 rotation the more pronounced the deviation. 



In their rolling gait the larvae tend to keep the back turned upward — that is, toward 

 the surface illuminated by the vast expanse of sky — while the head is bent downward 

 toward the region of shadow. When this position is maintained the eyes are illumi- 

 nated in a peculiar manner. At their most elevated points, opposite to the illuminated 

 surface, there is a lighted area, while at their most anterior ends, which are directed 

 toward the regions of obscurity, there is an area of shadow. 



"All of these observed movements," says Bohn, "such as repulsion and attraction, 

 rolfing and other rotations, are made with rapidity and precision and have the char- 

 acter of irresistible movements, according to laws which appear very exact, but which 

 vary with the physiological states." Bohn concludes that the larvae are guided in their 

 movements mainly bv the stimulus of light which enters the eyes, and that the eye acts 

 before the "otocvst" as an or^an of orientation . 



In regard to the question of any real distinction between the photopathic and 

 phototactic response, or between the intensity as distinguished from the direction of 

 fight, Hadley remarks that the direction of the light is effective in determining which 

 eye shall be stimulated most and what parts of both eyes shall be stimulated equally. 

 In the first instance the long axis of the body is swung into line with the rays, so that 

 both eyes are equally affected, while in the latter the body is so placed that the anterior 

 lateral surface of the eyes receive the strongest and the posterior lateral surface the 

 weakest illumination. 



Hadley found that when bfinded in one eye the larvae rapidly rotated on its long 

 axis in a definite direction or performed "circus" movements, moving in circles, toward 

 or away from the position of the uninjured eye according as the animal was negatively 

 62399°— II 14 



