THE AMERICAN LOBSTER. 
27 
shore. This is explained, he thinks, by the current and by the rise of the tides in the 
straits of Northumberland, which make the southern water cooler, and hence delay 
the spawning ( 209 , p. 233). 
Nielsen finds that the temperature of the water along the coast of Labrador ranges 
very low and does not exceed 40.05° F. on the warmest summer days. The lobster is 
thus debarred from this coast north of Henley Harbor, where it comes more directly 
under the influence of ice and the arctic current (see p. 15). 
SENSIBILITY TO LIGHT. 
The lobster is essentially a nocturnal animal, exploring the bottom in the quest of 
food mainly in the night, when it is far more active than during the day. This can be 
proved by anyone who watches their habits in aquaria or in lobster ponds or cars. It 
is true that they show some activity in the daytime, especially if they are fed, but at 
night they become very restless. Moving nimbly about, they explore every part of the 
car or investigate anew the resources of the aquarium. I believe that the eggs are 
laid and that the pairing takes place at that time, and this inference is strengthened 
by the fact that this is the common habit of shrimp and many other Crustacea. The 
crayfish, according to Ohantran ( 37 ), usually lays its eggs in the night. 
According to Forel, light can not penetrate in the ocean below a depth of 400 meters 
of tolerably clear water, but even in 50 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 bottom, which lobsters frequent in summer, and where we 
may expect to find the greatest difference between their diurnal and nocturnal habits. 
The lobster, like many other marine invertebrates, is very sensitive to the extremes of 
heat and cold. If exposed to direct sunlight out of the water, or to the nipping air 
of a winter’s day, it weakens and succumbs in a short time. 
The large floating cars in which lobsters are generally stored alive, 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 always suffer and sometimes die in 
consequence. The majority of lobsters probably spend the greater part of the year 
in depths where the effect of sunlight is but very 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 the adults would avoid intense sunlight 
The effect of light upon the colors of the shell is considered in another place. (See 
pp. 135, 136.) 
DIGGING AND BURROWING HABITS OF THE LOBSTER. 
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 at least, as 
extensively as the muskrat. I have observed this interesting habit only in lobsters 
confined in pounds where they are obliged to adapt themselves to new conditions, it 
is true, but since they burrow while in these inclosures in summer as well as in winter, 
we may infer that the habit is one which is often practiced when the animal is free to 
roam at will. This has been observed, moreover, by fishermen who have frequently 
taken lobsters from their holes. 
