THE STRUCTURE OF XES'IA HICKSONI. 221 



siphonoglyph, the cells of the lower half or third of which bear flagella. 

 This does not agree with the observations of Hickson (1883, p. 696), on 

 a specimen of Heteroxenia, in the siphonozooids of which he found a 

 well-marked siphonoglyph, but in the autozooids a complete absence 

 of siphonoglyph. 



The siphonozooids possess the usual eight mesenteries, but they are 

 extremely thin, and retractor muscles are not visible upon them. The 

 dorsal mesenteries bear mesenterial filaments (Fig. 39, D.M.F.), which 

 run in a sinuous course down the dorsal side of the polyp, and a short 

 distance into the portion of the coelenteron contained in the stem. The 

 coelentera of these siphonozooids cannot be traced more than two 

 millimetres into the stem. At this depth the coelentera terminate in 

 connection with one or more of the numerous endodermic canals. 

 Ova are not present in any of these coelentera. 



Stem. — No definite superficial endodermic canal system is distinguish- 

 able on the summit of the stem, except at its edge, where the young 

 buds appear to originate from it. It is, however, present in the cylin- 

 drical portion of the stem, and has a similar appearance and relations 

 to the corresponding canal system of Xenia Hicksoni. 



The longitudinal canals are developed to a much less extent than in 

 Xenia Hicksoni. They are small, and their lumen is often almost 

 obliterated. Canals are most numerous in the upper part of the stem, 

 especially in and immediately below the portion penetrated by the 

 coelentera of the siphonozooids. In this region of the stem there are 

 very numerous short transverse canals which place the various coelentera 

 in intimate communication with each other. 



The Origin and Internal Structure of the Buds of 

 Xenia Hicksoni. 



In this specimen the buds or young polyps arise on or just under the 

 edge of the umbrella-shaped area at the end of the stem. In most 

 other species of Xenia the buds generally arise in a similar position, 

 but in two of the colonies I have examined, and in three of the new 

 species described by Schenk (1896), buds occur not only round the 

 edge, but a few also on the middle portion of the expanded end of the 

 stem. The buds are much more numerous on the edge of the summit 

 of the stem and in Xenia Hicksoni, and, in fact, in most specimens the 

 buds are found only in this position. 



