Fewkes.] 296 ; [October 1, 
their polyps, and then leisurely dropping into their extended position 
with great facility. The highly contractile stem of the Rhizophysa 
shortens itself into a shapeless snarl, bringing with it feeding polyps. 
and tentacles into a tightly coiled mass. In this condition, however, 
it remains but an instant, and the closely drawn spiral is gently 
uncoiled, and one after another of the tentacles gracefully extend to 
their normal condition. Gegenbaur gives the length of the stem of 
the animal as 14 ft.; certain individuals, however, reach much 
greater lengths, and some of the specimens I have studied measured 
three feet at least. The diameter varies in different positions along 
the axis. Directly under the float the stem is very small, and it 
increases gradually to the very distal extremity. For a Siphono- 
phore of its size, the diameter directly under the float is very small 
as compared with other Physophoridae. A slight stem of the char- 
acter found in Rhizophysa could not support swimming bells and 
covering scales so much developed as in Agalmatopsis or Halistemma. 
The air-bladder or float of the Rhizophysa differs in one respect 
from that of any other Siphonophore. Enclosed in an enlargement 
of the stem, as that of the others, it has, from its under portion, 
branched and simple saccular appendages, which hang down from 
its lower surface. That into which they open is a very peculiar 
supplemental float, surrounding its lower hemisphere. As far as I 
am acquainted with the Physophoridae, these sacs are a peculiarity 
of Rhizophysa. Their function is unknown. They are wanting in 
certain Rhizophysidae described by Studer. The float has an 
opening into the surrounding medium, and the air can be expelled 
at the will of the animal. Gegenbaur saw the escape of air from 
the float when pressed, notwithstanding his previous declaration of 
its impossibility. This was first seen by Huxley. I have observed the 
float contracted, the air expelled in bubbles, the walls of the opening 
being at the same time protruded in a funnel-like structure. The 
opening is surrounded by dark crimson pigment spots, arranged with 
some regularity, and of polyhedral shape. I think they belong to 
the air-bladder, and are not on the external envelope. There is no 
opening from the float into the cavity of the stem. The float on the 
surface of the water always lies at right angles to the stem, as is 
shown in figure 2 of the plate. In this way the opening into the 
cavity does not lie at the apex of the animal, but at one end of the 
float. When we compare the float of Physalia with that of Rhizo- 
physa, we find the opening in an homologous position at one end of 
