LIFE HISTORY OF THE BLUE CRAB. 103 
Adult crabs which were kept in floats were found to become sluggish and to take 
no food after the temperature of the water fell to about 50° F. A juvenile crab, No. 6 
of Table B, was secured on February 25 and kept until April 20 in the laboratory, where 
the temperature of the water in the aquarium varied from 44° to 55° F. No moltings 
occurred. Other experiments, carried out during the summer, proved that crabs will 
molt freely in aquaria in the laboratory. Binford’s work also shows the same to be true. 
On April 20 this crab was placed in a float in the water of the bay, the temperature of 
the water being 60° to 65° F. On May 5 thecrab molted. Very probably crabs do not 
molt during the season when the temperature of the water is less than 60° F. From 
temperature records of the water of Chesapeake Bay, kept throughout the year, it has 
been found that between about the last week of October and the middle of April the 
temperature of the water is below 60° F. 
The bulk of the young crabs of Chesapeake Bay hatch during the last two weeks 
of June and the earlier part of July. From that time until the last part of October 
four months elapse. During this time the crabs pass the first two stages and reach 
probably about the ninth or tenth crab stage, attaining a width of about 1.25 to 1.50 
inches. Then come the winter months, during which time the crabs most probably 
do not molt, but lie dormant on the bottom. Growth and molting are resumed about 
the middle of April or the first of May. During the next three and one-half or four 
months the crabs molt five or six times and reach maturity during the last part of 
July or in the month of August. This agrees with the fact that during the six weeks 
from the middle of July to the last of August most of the pairs of mating crabs are 
found. As is described more fully on page 104, this occurs in the female at the 
time of the last molting and is thus a sure index of her arrival at the adult stage. 
The best evidence we have, then, points to the probability that the crab reaches 
the adult stage about 13 or 14 months after hatching. If, for example, a crab is 
hatched during June, it will reach the adult stage and mate during the latter part of 
July or the month of August of the following year. 
After leaving the megalops stage the abdomen of the male assumes the character- 
istic | shape, which is found throughout the remaining term of his life. The abdo- 
men is broad at the line of attachment with the body, but curves in shortly to anarrow , 
portion (Pl. LIV, fig. 35), which lies in a groove in the middle of the lower side of the 
body. Plate LIV, figure 34, represents the adult male crab when viewed from above. 
The abdomen of the female, after she leaves the megalops stage, is broad at the 
base of attachment and tapers to a point, each side forming almost a straight line 
(Pl. LIII, fig. 32). It lies in a depression on the lower side of the body and is held 
quite firmly in place by a pair of hooks which project from the body into cavities in 
the sides of the abdomen. ‘This form of abdomen is found in each stage of the female 
until adult size is reached. At the molting from which the crab emerges as an apparent 
adult the abdomen changes to almost a semicircular shape, except for a small point 
at the tip (Pl. LIII, fig. 33). It no longer lies in a depression of the body, and 
there are no hooks. It is held against the body by the effort of the muscles alone. 
The swimmerets seen on the under side of the abdomen, when it is pulled away from 
the body, are large and conspicuous (Pl. XLIX, fig. 16). In the pointed form these 
are small and insignificant in appearance. Plate LIII, figure 31, gives a view of the 
adult female when seen from above. It will be noted that the body is relatively longer 
