1881.} The Siphonophores. 773 
instructive study of these forms of life. Let us, therefore, con- 
sider in turn the more important genera allied : 
to Agalma which constitute the so-called Phy- ‘ y ord 
sophoride. 
One of the simplest members of the group } 
is a genus in which we have present, as it were 
the mere skeleton of the Agalma, or simply 
the float and the stem. To this stem is added ) 
feeding polyps and sexual-bells, while all other pon 
appendages, as necto-calyces, covering-scales, 
‘tasters’ and the like, are wanting. It is, in | 
fact, as if the Agalma had dropped all such as 
superfluous, and retained only those parts nec- i 
essary for its life; polyps to eat for the com- 
munity, a float to support the stem in the 2 
water, and sexual organs to reproduce new e--4 
colonies. We are to consider a genus which 
is one of the simplest, and on that account | 
Can very properly be described in this place. : 
The name of the animal to which reference ‘ 
is made, is Rhizophysa, which is one of the 
rare Siphonophores of the Mediterranean and 
other seas. Its bizarre form and simplicity of 
Structure gives to it an interest secohd to none 
of the Physophoridz, and as is the case with a 
_ Study of all aberrant forms, a few words about 
its general anatomy may do something to bring 
about a better understanding of the group of 
jelly-fishes, of which Agalma may rightly be , 
regarded a representative. The body of Rhizo- 
Physa is a simple, flexible, transparent tube, 
at one end of which is a float (a), Fig. 11, filled 
with air to support it in the water. This tube, 
besides being extremely flexible, is highly 
Muscular, and can be contracted into a shape- 
less snarl under the air bladder, or elongated 
_ dnto-a Straight, transparent, thread-like axis, Fic. 11. — Rhizo- 
. 38 shown in the figure. Sensitive to the least | PAYS. 
_ touch of a foreign body, it is seldom quiet, contracting or ex- 
_ Panding its length by muscular action of the stem walls. Inno 
