Appendix to Cionistes reticularis. 281 
the Hydroidse, any phase — plaimloid, polypoid, or medusoid 
— may be absent. 
The perfect several-lipped Medusa appears to be a sym- 
metrical organism composed of eight or more elements, each 
element corresponding to the half of a lip. Each of these 
elements is composed of three subelements, the alimentary, 
reproductive, and prehensile, any of which may be sup- 
pressed, or unite with others of different value on the same 
element, or of the same value belonging to neighbouring 
elements. Thus, in Sarsia the peduncle appears to consist 
of a single alimentary subelement, and the single reproduc- 
tive element or generative sac extends around and along the 
whole of it except the single trumpet-shaped lip. This lip 
is occasionally placed on one side and at some distance from 
the extremity of the peduncle, indicating the asymmetrical 
character of the latter organ in this genus. In Euphysa and 
EleutJieria the ovisacs coalesce, and are placed within and at 
the base of the peduncle. Steenstrupia and Saplienia furnish 
examples of the suppression of certain of the marginal ten- 
tacles or prehensile subelements, and the exaggeration of 
others. 
The Polyp of the Hydroid Zoophyte must also be con- 
sidered as composed of one or more elemental zooids. Thus 
we have the zooid of a single element in the ' tentacular polyp ' 
of Hydractinia ; the zooid of two elements in the two-ten- 
tacled and two-lipped Lar Sahellarum (Gosse) (PI. XII. fig. 
8), and in the minute two-lipped and non-tentacled polyp 
which occurs on the Antennularias and others ; the zooid of 
several elements in the five-lipped polyp of Trichydra 
(T. S. W.) ; that of many elements in the polyp of Tubula- 
ria indwisa, which I have elsewhere shown to be formed by 
the confluence of the several distinct tubes of which the po- 
lypary or coenosarc is composed, each of which tubes may be 
traced, by its coloured endodermal ridges, to the mouth of 
the polyp, and bears its own system of tentacles and repro- 
ductive apparatus. 
The compound character of the polypary is also seen in 
Halecium and Antennularia, and in a very beautiful manner 
in the very early state of Sertularia pumila, whicli (after it 
