184 ' BULLETIN OF THE BUREAU OF FISHERIES. 



th e 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 t o e xpect, 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 adolescen t 

 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 40 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, ^he 

 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 

 ani mal has become sensitive to a minimiin) Quantity of light. For this rea-snn ainnp w^ 

 should expect that adults would tend to avoidJxi terisg .s unlight. 



BURROWING HABITS. 



The lobster not only dig^.s up the sea, bottom in its search for shellfish and covers itself 

 with mud in cold weather , b^^^^fij^s. »]T fjfr^snrnp^ ^ c:onditio ns 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 



