8O J. E. DUERDEN. 



assumed for the various members of a cycle, according to their 

 relation to the members of the inner cycles. 



Professor A. Schneider in 1871 and Professor C. Semper in 

 1872 also discussed the same subject. The former agrees with 

 Milne-Edwards and Haime as regards the manner of develop- 

 ment of the first three cycles : first a cycle of six appears, then a 

 smaller cycle of other six alternating with the first, and later a 

 cycle of twelve septa which are smaller and alternate with the 

 twelve making up the first and second cycles. In the further 

 growth Schneider considers that the septa of a newer cycle may 

 so enlarge in size as to appear to belong to an older cycle, and 

 thus the primary sequence and hexamerism become lost. 



Semper holds that no constant rule for septal development can 

 be established, that the manner of growth varies more or less 

 with each species. 



Professor G. von Koch, in the course of his prolonged studies 

 on the morphology of corals, has also made certain observations 

 upon the laws of septal development, particularly in his paper 

 " Das Vermehrungsgesetz der Septen," 1881. His results are 

 based mainly upon serial sections of individual coralla of Caryo- 

 phyllia, and lead him to conclude (p. 93) in the main in favor of 

 the validity of the sequence given by Milne-Edwards and by 

 Schneider : " Bei den sechszahligen Korallen, sowohl den Epo- 

 rosen als den Perforaten, wachst die Zahl der Sternleisten (Septa) 

 in der Art, dass sich nahezu gleichzeitig im ganzen Umfang des 

 Kelches zwischen je zwei alteren eine jungere anlegt, also die Zahl 

 der Sternleisten eines folgenden Cyclus immer gleich ist derSumme 

 aller vorher vorhandenen. Alle Ausnahmen von dieser Regel sind 

 auf direxte Anpassungen oder erblich gewordene Veranderungen 

 im Wachsthum des ganzen Thieres zuruckzufuhren." 



All the above conclusions are based mainly upon the examina- 

 tion of adult coralla, in \vhich there is available for comparison only 

 the relative sizes of the septa and their order of appearancein serial 

 sections. The actual details of growth of the septa indeveloping 

 corals, in their relationships to the mesenteries, have in no instance 

 been followed beyond the first two cycles. Professor H. de La- 

 caze-Duthiers (1873, '94, '97) and Professor G. von Koch (1882, 

 *97) have both studied the early development of the skeleton in 



