IOO J. E. DUERDEX. 



individually. Any cycle of septa or mesenteries tends to attain 

 its radial condition before the next cycle commences to form, 

 when the additions take place in such a manner as to again con- 

 fer bilaterality upon the polyp as a whole. Thus the first two 

 cycles of septa become truly radial before an additional cycle 

 commences, when the growth of this is continued in a bilateral 

 manner ; likewise the new second and third cycles assume their 

 radial stage before the members of the fourth cycle made their 

 appearance, these also proceeding from one border to the other. 

 In like manner the first cycle mesenteries are nearly radial before 

 those of the second cycle arise and introduce a conspicuous 

 bilateral symmetry ; on the second cycle mesenteries assuming 

 the radial plan the third cycle members begin to appear, again in 

 a bilateral manner. 



The successive dorso-ventral growth followed by the constit- 

 uent mesenteries and septa of each cycle also confers a certain 

 individuality upon the cycle. The different cycles, arising inde- 

 pendently, seem to represent so many distinct recurring phases 

 of growth in the life of the polyp ; they do not constitute a con- 

 tinuous addition from one border to the other, as is usual in per- 

 manently bilateral animals, particularly segmented forms. The 

 members of a cycle appear in a dorso-ventral sequence and may 

 retain their differences in size for a long time, but in the end they 

 become equal and thereby confer radial symmetry upon the 

 polyp. Then another cycle commences to form in somewhat the 

 same bilateral dorso-ventral succession, displays for a time the 

 consecutive origin of its members, and afterwards attains radiality. 



The conception of recurring phases of growth in cyclic coral 

 polyps is best realized when comparison is made with the mesen- 

 tenal increase characteristic of the Ceriantheae and Zoantheae. 

 In the former the mesenteries beyond the protocnemes always 

 develop in a regular bilateral successive manner, from the dorsal 

 (anterior, sulcar) to the ventral (posterior, asulcar) aspect, the 

 oldest being dorsal or anterior and the youngest ventral or pos- 

 terior, recalling more the method followed by segmented animals ; 

 there is in the Ceriantheae never a reversal of growth to the ante- 

 rior end, followed by a successive series to the other, such as 

 occurs in ordinary hexactinians. Employing the term " band of 



