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BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



what oblique, and club-shaped, and as short as it is distant from the polypidian 

 tubes; second, of a large, transverse, and cylindrical part. The orifice on the 

 dorsal of the zoarium is polygonal and on fossils always open. 



When a tergopore is aborted (fig. 202 A), it is immediately replaced by two 

 others, formed by the simultaneous bifurcation of the distal and proximal tergo- 

 pores. 



Cx12 



Dx12 



B x25 



A "25 



FIG. 202. Tergopores. 



A. Longitudinal thin section of Jtesonea subpcr- 

 tusa, new species, X 25, illustrating structure of ter- 

 gopores (to right) and zooecial tubes. B. Transverse 

 section, X 25, of the same species showing the 

 zooecial tubes in the upper half and the tergopores 

 below. C. Broken branch of same, X 12, with the 

 layer of the tergopores separated from the zooecial 

 tubes. D. Dorsal of same, X 12, exhibiting large 

 tergopores. 



FIG. 203. B'irmatopores. 



Longitudinal thin sec- 

 tion of Idmidronea coro- 

 iiopus Milne Edwards, 

 1838, illustrating struc- 

 ture of firmatopores (to 

 right). 



The ectocyst of the tergopores was much thicker than that of the polypidian 

 tubes, for its disappearance shows a much larger, interzooeoial space (fig. 202 A). 



As the tergopores give rise to one another independently of the polypidian 

 tubes, their ensemble is easily separated from the frontal of the zoarium (fig. 

 202 C). They evidently form part of the system of basal fixation of the zoarium. 

 Tn sections, they have the appearance of mesopores but they differ in their forma- 

 tion for these are tubes and not ramifications. 



