118 BULLETIN OF THE BUREAU OF FISHERIES. 
parent membrane, which is probably a means of protecting them from the action of 
the sea water, by which they are surrounded. It seems probable that the eggs lack 
this tough membrane until after they have passed through the sperm sacs and have 
been penetrated and fertilized by the spermatozoa which are found there. 
Interval between copulation and spawning.—The length of time which elapses between 
copulation and the laying of the eggs depends on the season at which copulation occurs. 
Experiments which were performed in the endeavor to throw some light on this question 
follow. 
On various dates between June 18 and 26, 15 adult female crabs were selected 
and confined in floats for observation. By the external appearance it had been as- 
certained that these crabs had molted for the last time within the previous few days. 
Such crabs can readily be distinguished after a little practice by their fresh, blue color, 
the weakness of the muscles holding the abdomen against the lower side of the body, 
and the bright, clean, slightly golden appearance of the swimmerets. At the same time 
several such females taken from the same catch were dissected and found to have 
copulated. It was assumed that those selected for the experiment had also copulated. 
During the course of the experiment the crabs were fed with fresh fish. On August 1 
one female threw out a very few eggs. About August 15 two others each formed a 
sponge, the eggs of which hatched from the 27th to the 30th. In general, it was found 
in all experiments with female crabs confined in floats and crates that only a small 
percentage of such individuals spawned. The confinement was apparently prejudicial 
to the full exercise of their natural functions. In the case of the three individuals 
which did spawn it will be seen that the interval between copulation and spawning 
was about two months. 
Further, on June 20, a female crab with the triangularly shaped abdomen was 
confined in a float with a male. On June 25 it was found that the female had molted 
and had the broad abdomen. Presumably she had mated, although the act had not been 
observed. The male was removed. On August 27 it was found that the female had 
thrown out a small sponge within the preceding two or three days. Upon microscopic 
examination the eggs were seen to have begun development, showing that mating had 
occurred and that they had been fertilized. In this case also about two months elapsed 
between copulation and spawning. 
The facts just mentioned apply, however, to the fairly small percentage of female 
crabs which mature in June or the early part of July, and more especially to those of the 
southern part of Chesapeake Bay, since not many mature before the middle of July at 
points farther north in the Bay. Earlier in this paper it was shown that the most of 
the mating occurred from the middle of July to the last of August and that the female 
crabs migrated to the southern part of the Bay and spent the winter on the bottoms 
thereof. Later it is proved, page 119, that these crabs spawn the following June 
and July, thus accounting for the abundance of sponge-bearing crabs found in the 
late spring and summer in the southern part of the Bay. In this case the period elapsing 
between copulation and spawning is about 9 or ro months. During the winter the crab 
is inactive, eating very little or nothing. Its natural functions are therefore practically 
suspended, for it remains in a state of semihibernation. 
