104 BULLETIN OF THE BUREAU OF FISHERIES. 
from beak to abdomen than that of the male and that the claws are smaller. The 
adult male can usually be distinguished from the female by these characteristics with- 
out the necessity of examining the abdomen. 
It is most probable that this molting, in which the change in the abdomen is 
involved, is the last one which the female undergoes. Adult females were kept under 
observation for several months in crates and floats. None was observed to molt during 
this time. Immature crabs molted when kept under similar circumstances. In the 
region of Crisfield, Md., the center of the soft-crab industry, hundreds of thousands 
of crabs are caught shortly before molting and kept until it occurs, in order to secure 
the soft crabs for the market. The author examined 2,624 cast shells obtained from 
various ones of the floats in which such crabs are confined. Not one of these shells 
bore the broad abdomen of the adult female. No crabber was found who could recall 
ever having seen a cast shell bearing the broad abdomen. Females with broad abdo- 
men are virtually never found exhibiting the-easily recognized marks that distinguish a 
crab which is preparing to molt. Three crabbers were found who said they had seen one 
or two adult females bearing such marks, but that they did not molt when kept in the 
floats. It is very doubtful if the marks observed on the crabs in question were really 
the same as those that characterize a crab in the premolting stage. 
As no such change occurs in the abdomen of the male, we have no criterion other 
than that of size, general appearance, and the manifestation of sexual activity by 
which to judge its probable state of maturity or whether it molts again after reaching 
maturity. The average maximum size is, as stated above, about 614 to 7 inches. It 
is probable that the males become sexually active somewhat before attaining the maxi- 
mum size, although the evidence on this point is rather meager. Both male and female 
crabs are found, especially during the winter, whose shells are discolored and bear 
barnacles, oysters, etc., apparently giving evidence that the shell has not been cast 
for a considerable period of time. There is no especial reason to suppose that the 
male molts indefinitely, in contradistinction to the female, which most probably does 
not. 
MOLTING. 
As already stated, the crab increases in size only when it molts, or sheds its shell. 
It is not exactly true to state that the crab grows only when it molts or that it grows 
by molting. It molts because it has grown and the shell, being inelastic, is too small 
and is thrown off.¢ Thus there is a sudden abrupt increase in size due to the expansion 
of the organism which has previously been crowded and somewhat wrinkled up within 
the old, hard shell. 
The actual molting process has been described by Hay.’ His excellent photo- 
graphs illustrating some of the stages of the process are included in the plates appended 
to this paper. The account given in this paragraph is modeled to some extent after 
his description, although an effort has been made to present the matter in more detail 
than he employed. As the crab approaches the molting period it begins to show its 
condition by various external markings, or signs. The first indication is the appear- 
ance of a narrow, black line just within the thin outer and back margins of the two 
@ Herrick, op. cit., p. 200, b Hay, op. cit., p. 411. 
