126 
BULLETIN OP THE BUREAU OF FISHERIES 
u 
p. 
< 
c 
f-i 
3 
to 
o 
1895 
1896 
1897 
1893 
1899 
1900 
1901 
1902 
1903 
1904 
1905 
1906 
1907 
Fig. 29. 
from 1 to 3 inches in diameter. Shortly after this they disappeared. The disap- 
pearance probably took place when all strobilization had stopped and the currents 
carried the medusae away. Occasionally at a later date swarms of large adults have 
been seen in Vineyard Sound or Buzzards Bay. No adults were noted during the 
past summer (1923) in local waters, although large swarms of mature Aurelia were 
seen on two occasions in neighboring localities — Mount Hope Bay on July 14, and 
at the entrance of Oyster Bay in early August. 
It is difficult to understand how the planulse get back into the harbors (particu- 
larly Waquoit Bay) in such large numbers when apparently no adults remain in the 
region. The eggs can not be deposited before 
the medusae leave in the summer because the ani- 
mals are not mature at the time. I have never 
seen a mature specimen in Waquoit Bay. There 
seem to be but two possibilities — either enough 
adults remain in the bay until the breeding season 
(perhaps on the bottom) to repopulate it or the 
planulse are drifted in by the tide. I believe that 
the first assumption is more probable; that is, that 
sufficient adults remain to restock the waters even 
though none may be seen at the surface. The dif- 
ficulties besetting the second possibility make it 
almost impossible except under rare conditions 
when Vineyard Sound is filled with adult Aurelia 
at the correct time. In the first place the medusae 
are entirely at the mercy of the winds and tides. 
They may be widely scattered in coastal waters 
or pUed together in great banks, as described by 
Hargitt and Agassiz. The latter author consid- 
ered that the animals gathered together in the 
breeding season, but this is not probable. After 
storms large numbers of disks, minus lobes and 
tentacles, of both Aurelia and Cyanea are often 
found at the surface in local waters. All are de- 
stroyed before winter arrives. As the sexes are 
separate in Aurelia it is largely a matter of chance 
whether fertilization takes place at all, because the 
adults are likely to be widely separated before reaching sexual maturity. Under 
these conditions it would hardly be possible for the species to maintain itself, because 
it is apparently beset with more difficulties than the cod and has a proportionately 
much smaller number of eggs. Therefore, the few adults that remain in the bays 
may serve to maintain the species during seasons when fertilization in the open 
waters is impossible, while a fortunate gathering of adults during the breeding 
season may account for the enormous swarms present in certain years. This 
dependence on a chain of circumstances to bring the sexes together at the right time 
probably goes far to explain the irregularities in this and allied neritic species. 
■ 
1 
1 
B 
I 
1 
■ 
1 
1 
1 
1 
1 
1 
—Occurrence of Aurelia flaoidula during 
successive years, 1893 to 1907 
