336 



Dr. H. A. Nicholson on the Minute 





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Thin sections of Heteropora neozelanica, Busk (recent). A. Part of a 

 tangential section taken just below the actual surface, enlarged fifty 

 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 zocecia in the axis of the stems, the comparative paucity of inter- 

 stitial 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 zocecia. The section shows distinct cross par- 

 titions (or "tabulae") crossing the cavities of the tubes towards the 

 deeper parts of the branch, as also the canaliculi crossing the walls, and 

 the pores representing the openings of these on the backs of the tubes. 

 D. Part of a transverse section in its outer portion, where the zocecia 

 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 zocecia ; b b, the interstitial tubes ; c c, the walls, with the con- 

 necting canaliculi. 



