No. 394.] HYDROID FROM LONG ISLAND SOUND. 805 
The medusa (Fig. 4) represents a stage in organization that 
occurs but seldom among the Hydromedusz. When it is 
liberated the sexual products, borne on the very large manu- 
brium, are fully matured, so that the medusa after its liberation 
does not nourish and develop the former, but only distributes 
them. This done, the medusa dies, after its free-swimming 
life of a few hours. Its organization is quite simple, a condi- 
tion to be expected both in connection with the recent libera- 
tion and its transitory existence. So far as could be determined, 
from the very rudimentary condition or absence of the characters 
usually employed in classification, it belongs most nearly to 
Haeckel’s Dysmorphosa type, in which the mouth parts and 
tentacles are simple, the latter eight in number. 
Though the medusa has most of its structures degenerate, it 
is still distinctly a medusa. As seen in side view (Fig. 4), 
it is somewhat higher than wide, its vertical diameter being 
about I mm. Into the cavity of the bell hangs the very large 
manubrium, which is gorged with sexual cells. There is no 
mouth opening and no lips nor tentacles around the mouth 
region. From the upper part of the stomach pass the four 
radial canals which connect with the circular canal at the edge 
of the bell. From the outer edge of the umbrella project eight 
equal rudimentary tentacles, four paradial and four interradial. 
They bear numerous stinging cells, but eye-spots seem to be 
absent. From the inner edge of the bell projects the narrow 
velum. Lining the subumbrella there is a well-developed 
layer of muscle fibres, and though degenerate in most ways, 
the medusa swims actively during the few hours of its free 
life. 
In my specimens the medusz were liberated in the evening, 
soon after dark, and though it would not be safe to conclude 
that this always takes place, I am inclined to think that it does. 
In a species of another hydroid (Pennaria) which the writer 
observed in Jamaica, and in which the medusz likewise lead a 
free life of but a few hours, the latter are liberated within an 
hour after dark, at almost exactly the same time from day to 
day. I think the same may be found to hold for the form here 
described. 
