184 
BULLETIN OF THE BUREAU OF FISHERIES. 
the cover of darkness, either at night or in early morning. Such indeed is known to be 
the common habit of crayfish, shrimp, and many other Crustacea. 
While the lobster is very sensitive to light throughout every stage of its existence, 
its reactions to this stimulus are of a complex character, especially during its free swim- 
ming career, as will be seen in a later chapter. It will appear that the young shun or 
avoid light of a greater intensity or move toward or away from a source of light and in 
the direction of its incident rays as a result of the varying state of the animal itself and 
of its environment. There seems to be ever a struggle among competing impulses, now 
one set of reactions winning the day, now another. In general the young seem to seek 
the light, as their swimming habits might lead us to expect, and are usually captured in 
the day time, but they are sometimes caught at night. 
After the discovery of the bottom has been made, through all their later adolescent 
and adult stages they practice concealment, and prefer the twilight of their rock caves or 
tangles of weed amid the sand. Yet, under exceptional conditions, the adult may 
expose itself to stronger light. 
According to Forel, light can not penetrate the ocean below a depth of 400 meters 
of tolerably clear water, but even in fifty fathoms off the Atlantic coast the difference 
between day and night can not be very considerable. This is not the case in shallow 
bays or sounds with sandy bottoms, which lobsters frequent in summer, and where 
we may expect to find the greatest difference between their diurnal and nocturnal habits. 
The large floating cars in which lobsters are generally stored in readiness for market 
are always kept closed. When they are particularly shallow and the lobsters are exposed 
to the glare of the sun they are sure to suffer, and sometimes die in consequence. The 
majority of lobsters probably spend the greater part of the year at depths where the 
effect of sunlight is but slight, and during the course of its evolution the eye of this 
animal has become sensitive to a minimum quantity of light. For this reason alone we 
should expect that adults would tend to avoid intense sunlight. 
BURROWING HABITS. 
The lobster not only digs up the sea bottom in its search for shellfish and covers itself 
with mud in cold weather, but burrows under some conditions as extensively as the 
muskrat. Impounded lobsters will sometimes burrow during both summer and winter, 
and this habit is no doubt freely practiced when they roam at will. 
The burrowing habit was typically shown in one of the pounds at Southport, Me., 
where the lobster holes were driven horizontally into a mud bank for a distance of from 
I to 5 feet. When we did not see the feelers and claws of a lobster projecting from its 
hole, the occupant could usually be felt by inserting the end of an oar, and it would 
sometimes grip the blade and allow itself to be dragged out clear. 
The holes had an opening of from 8 to 10 inches in diameter, which allowed of 
their being readily probed and measured with an oar blade. I did not observe that 
they ever had an upward or downward curve, but they sometimes swerved to the 
right or left, which might be due to the presence of some obstacle in the path. In 
