124 AMERICAN FOSSIL BRYOZOA. [bull. 17.1 



is parallel to the surface and close enough to it to show the structures 

 developed in the peripheral region. Of bifoliate forms two tangential 

 sections are needed, one close to the surface and another near the 

 middle (mesotheca), though often one tangential section may be made 

 so as to show all the features. 



Care must be taken to select specimens that have not suffered from 

 compression. Sections of specimens compressed or otherwise dis- 

 torted have occasionally given rise to grave errors, as, for example, 

 when Waagen and Wentzel, misled by sections of specimens of the 

 Fistuliporidse with the axial region crushed, believed they had found 

 evidence of the development of zooecia from the intermediate coenen- 

 chymal (vesicular) tissue. 



