j M M r Q 



II II 



/ I 



Fig. 7. Zoanthus, after Bourne. I-VI the first six pairs of mesenteries ; 

 7-9 couples added later. 



Fig. 8. Cerianthus, based on the work of Boveri and Bourne. Numerals 

 and figures indicate the order of development of the mesenteries. 



Fig. 9. Hypothetical section across a young Streptelasma profundum 

 showing the original eight mesenteries ; the beginnings of the corallite are 

 indicated by the shaded part of the figure. 



- Fig. 10. View looking into the calyx of an adult Streptelasma profundum; 

 (republished from the Ann. N. Y. Acad. Sci., vol. xix, p. 55). The tertiary 

 septa are greatly exaggerated in apparent size because of the sloping walls of 

 the cup. These really extend but a small fraction of an inch from the wall 

 in toward the center of the cup. 



Fig. 11. Hypothetical cross section of a zooid to fit the cup shown in fig. 

 10. 1,1, etc., are the eight primary mesenteries. It is possible that all of 

 the mesenteries reached the stomodeeum. The dorsal member of each 

 couple is represented as incomplete because the tertiary septa, assumed to 

 have developed in the exocoeles, are always short and do not appear till late 

 in the life of the individual. 



