THE STRUCTURE OF XENIA HIOKSONI. 291 



tera of these siphonozooids cannot be traced more than two 

 millimetres into the stem. At this depth the coelentera ter- 

 minate 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 

 distinguishable on the summit of the stem, except at its edge, 

 where the young buds appear to originate from it. It is, how- 

 ever, present in the cylindrical 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 siphono- 

 zooids. 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. 



On examining a transverse section of the upper portion of a 

 stem of the colony, the coelentera in the peripheral portion of 

 the stem are seen to be smaller than those in the central 

 portion, and some of them are obviously the coelentera of very 

 young polyps (PI. 25, fig. 9, right). 



