HYDEOZOA. 
63 
float ; there are no swimming-bells or covering-pieces. Physalia Case 3, 
pelagica (Model, Case 3) has one long stout main tentacle and Upright part, 
numerous lesser ones ; Caravella * (Model, Case 3) has numerous 
large tentacles. The float is borne wholly above the surface, and is 
carried along by the breeze with the broad end foremost and the 
tentacles trailing behind. Prof. Agassiz saw specimens with tentacles 
over fifty feet in length. Physalia is notorious for its dangerous 
stinging properties. 1 
Rhodalia miranda * is a deep-sea Siphonophoran, wonderfully 
adapted for living at great depths ; the depressed oval air-sac is 
followed by several circles of swimming-bells each attached by a 
broad vertical lamella to the stem. 
A curiously modified swimming-bell, the anrophore, allows of 
communication between the air-sac and the water ; by emptying or 
secreting the air or gas the animal can sink or rise within certain 
limits without using its swimming-bells. The 64 stem ” is not a 
delicate tubular siphon as in Physophora , but forms a thick mass 
permeated by canals, the feeding polyps with tentacles and generative 
buds being attached to its lower surface. 
Most of the swimming-bells and all the tentacles have become 
detached in the specimen, the red colour of which is artificial ; 
but the air-sac and massive stem are well preserved. The specimens 
were obtained by the Challenger from a depth of 600 fathoms in 
the South Atlantic. 
Diphyes * (Fig. 24 a, b), which is without an air-sac, has two 9 ase 3 ’ 
swimming-bells, and below these groups of covering-pieces, feeding u P ri S ht P art ' 
polyps, and generative buds situated along the stem. 
In Velella* or “ By-the-wind Sailer ” (Case 3), a vertical semi- 
circular “ sail ” is attached diagonally across the upper surface of 
an oblong disk ; attached to the lower surface of the latter are one 
large central feeding polyp and circles of smaller feeding polyps, 
generative buds, and a marginal fringe of tentacles. Fleets of 
Velella sailing along in the breeze are more commonly seen in 
warm latitudes, but specimens, both of Velella and Physalia , have 
been found off the south-west coasts of England. 
P or pita * consists only of a circular disk with its dependent polyps 
and tentacles. 
1 Mrs. David mentions in her book on Funafuti that the natives are more 
afraid of Physalia than they are of the sharks. 
