NATURAL HISTORY OF, AMERICAN LOBSTER. 
355 
contact with solid bodies, began to assert itself and thus to modify the previous sensi- 
tiveness to light, apparently leading 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 
larvse of Homarus gammarus of Europe, reported in 1905. He believed that the newly 
hatched young were immediately attracted to the surface, since they are positively 
phototactic. At first they approached the light, 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 inclined to the 
right and left, sometimes as much as 90°. It can likewise 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 inclined to 
the right, the larva advanees by deviating to the right, and the more considerable the 
rotation the more pronouneed 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 peeuliar 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, 
rolling 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 coneludes that the larvae are guided in their 
movements mainly by the stimulus of light which enters the eyes, and that the eye acts 
before the “otocyst” as an organ 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 
light, 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 surfaee the 
weakest illumination. 
Hadley found that when blinded in one eye the larvse 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 
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