1881. ] The Siphonophores. 193 
stem its cavity is enlarged, and on that enlargement hangs a circle 
of covering scales not unlike what exist in the genus of Siphono- 
phores, called Physophora. The larva is now in a condition struc- 
turally not very distant from the adult. In minor details there 
are, as has been already pointed out, certain differences, but from 
this stage on the growth into the adult is direct and without the 
formation of provisional organs of any kind. 
A description of the development from the bud of each kind of 
characteristic structure found on the stem of the Aga/ma, would 
take me into details too special for this paper. It is sufficient for 
our argument as to the nature of the Aga/ma, to state that each 
and every structure along the stem originates as a simple bud, 
which can at first hardly be distinguished one from the other, 
39- ——_s 
Fic. 10.—Lissta octopunctata (young). 
whether they form float, swimming-bell, feeding polyp or cover- 
ing scale, In their earlier stages they are all alike. The details 
of the changes by which now a swimming-bell and now a float is 
formed are not necessary for my argument, and I will not con-_ 
sider them in this place. : 
I have already, in my former sketch of the anatomy of Aga/ma, 
made the comparison of the Siphonophore to a little medusa, 
called Lizzia, found in our waters. That comparison at which 
McCrady hinted long ago is supported by the embryology which 
I have just given. 
In the primitive medusa, as has been shown, we find a jelly-_ 
fish with parts identical with those of a Lizzia. All the organs 
