Appendix to Cionistes reticularis. 



281 



the Hydroidse, any phase — planuloid, 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 

 Eleutheria 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 Lav Sabellarum (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 Tricliydra 

 (T. S. W.) ; that of many elements in the polyp of Tubula- 

 ria indivisa, 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, which (after it 



