AFFINITIES AND ZOOIOGICAL POSITION 69 



such a section (fig. 9, a), we observe that it is generally quite 



l'"'g- 9- — Tliin sections of Hctcropoya ncozelaiiica. Busk (recent). A, Part of a tangential 

 section taken just below the actual surface, enlarged 50 times. The zooecia are cut 

 across in their outer thickened portion ; and the canaliculi traversing their thick walls 

 and communicating with the smaller interstitial tubes are well shown, as are the delicate 

 radiating spines projecting into the cavities of both the sets of tubes. B, Part of a 

 transverse section of a branch, showing the thin-walled angular condition of the zooecia 

 in the axis of the stems, the comparative paucity of interstitial tubes, and the total or 

 almost total absence of connecting canaliculi in this region (enlarged 50 times), c, Part 

 of the median longitudinal section of a branch (enlarged 18 times), showing principally 

 the outer thickened portions of the zooecia. The section shows distinct cross partitions 

 (or "tabulae") crossing the cavities of the tubes towards the deeper parts of the branch, 

 as also the canaliculi crossing the walls, and the po:es representing the openings of these 

 on the backs of the tubes. D, Part of a transverse section in its outer portion, where 

 the zooecia are laid open longitudinally (enlarged 50 times). The section shows the 

 peculiar structure of the thickened walls and the canaliculi crossing these. A few of the 

 delicate radiating spines are also seen, a a, The proper zooecia ; i> l>, The interstitial 

 tubes ; c c, The walls, with the connecting canaliculi. 



possible to distinguish the proper zooecia from the interstitial 



