Chap. 11. MEDUSOID BUDS OF CLAVA. 221 



SECTION II. 



THE MEDUSOID BUDS OF CLAVA LEPTOSTYLA. 



The medusoids of Clava leptostjla are the most simple of all the Tubularians 

 except those of Rhizogeton fusifoi-mis, which are almost identical in the arrange- 

 ment of their walls. (See PI. XX. Figst. 17-21.) They are simple, rounded, and 

 closed buds, attached to the main stem by a tapering pedicel, and may be compared 

 to incipient Medusa3-buds of the types in which the buds become true Medusae. 

 But in this genus they are not freed, and do not assume the form of an open 

 bell. In their most highly-developed state, there is only a single wall (PI. XX. 

 Fiffs. 11-15, a}) in the spheroidal buds, and this is homological to the disk or 

 umbrella of the spheroidal free MedusjB. This wall, when followed along its course, 

 becomes continuous Avith the outer wall {a) of the ^^edicel and the body. It is 

 of uniform thickness throughout, and equal, in this respect, to its continuation on 

 the pedicel and body. The only point where the walls may be said to be double, 

 is next the junction of the peduncle (« b), at what, homologically, is the top of 

 the disk of a common Medusa. From the base of the proboscis {d) its own single 

 wall dilates, and passes a short distance down the inner surface of the wall of 

 the disk, and thus forms a narrow, sharp-edged ring (i^), and, moreover, renders 

 the disk double-walled at this jooint. The pi'oboscis [d) projects through nearly 

 the whole depth of the bud, and is almost uniform in breadth throughout, there 

 being only a slight dilatation near its tip. It usually occupies from one fourth 

 to one third of the transverse diameter of the cavity of the bud. Its single wall 

 is as thick as that of the disk, and is uniform from tip to base, at which latter 

 point it dilates, as we have described above. There is no mouth at the tip of 

 the proboscis, nor any means of exit, for the circulating fluid, which bathes its 

 inner surface, excejst to return backward through the way by which it entered. 

 The cavity of the bud, in the males, is filled by the spermatic mass {Fig. 16, V^), 

 or, in the females, occupied by either two or three eggs {Fig. 11, h^), or segmented 

 masses {Figs. 12 and 13, h^), or planulae {Figs. 14 and 15, h^), according to the age 

 of the Medusoid. These imjierfect Medusa^, which, from their relations to their 

 Hydroids, are as truly Medusae as the Sarsite arising from Syncoryne, exhibit the 

 most striking resemblance to the so-called gonocalyx of the Siphonophoras. 



The pedicel, in connection with the medusoid, forms a pear-shaped figure, the 

 former constituting the narrowing, inverted, conical portion. The greater bulk of 

 this cone is formed by the inner wall {Figs. 11-15, b), which, at the base {U') of 



