DESIGN IN THE ORGANIC WORLD. 449 



and their openings at the margin forming but a single row of 

 pores (Fig. IV ., i, 3, 4). The arrangement of the first-formed 

 chamberlets, moreover, presented a single departure from the 

 cyclical plan, showing a distinctly spiral disposition (Fig. IV., 2) ; 

 tne mouth ol the spire, however, rapidly opening out by successive 



Ki.;. IV. 

 Disk of Sunplc Type of Orlntolite. 



1. Surface of Disk, showing later growth of concentric lings of chamberlets 

 around a first -formed spire. 



2. Central portion enlarged. 



3. Kdge of DUk, showing single row of marginal pores. 



4. Vertical Section, showing succession of chamhcrlcts communicating 

 with each other radially by passages in the annular partitions, and laterally by 

 the annular canal-, whose sections are seen as dark spots. 



additions, so as to enclose the &quot; nucleus ; after which all suc 

 ceeding additions were complete rings, so that the cyclical plan 



