102 



Dr. J. E. Duerden on the 



] rlmary complete directive mesentery adjacent to it (///) a 

 new pair of directives, the musculature being on the faces of 

 the mesenteries turned away from one another ; the next 

 incomplete and adjacent complete new mesenteries on each 

 side form a unilateral anisocnemic pair (Z>, C), in which the 

 musculature is on the faces turned toward each other, as in 

 pairs /and VI of the simple polyp. The two members of 

 the middle bilateral pair (i?, I)) of incomplete new mesen- 

 teries have as yet no corresponding complete mesenteries 

 wherewith to constitute a unilateral pair. The primary dorsal 

 (abaxial) directives (/F, IV) are somewhat widely separated, 

 but no new mesenteries are intercalated between them. 



With the exception of the presence of two stomodajal tubes 

 instead of only one, the disposition of the new mesenteries so 

 far exactly resembles the stage in the mesenterial increase in 

 Porites represented in fig. 3. 



Fig. 4. 



Transvor?e section through the stomodaeal region of an enlarged polyp, 

 wholly retracted within the corallum. The stomodasiim is divided 

 into two tubes, which are connected by two mesentery-like strands. 

 Four pairs of new mesenteries, A-D, are present in addition to the 

 six pairs in simple polyps. 



Special importance attaches to the two mesentery-like 

 strands which connect the two stomodaeal tubes. Sometimes 

 they are short, as in the section represented, or they may be 

 much longer, the stomodsea then being widely apart. For a 

 long time their significance was difficult to understand, and it 

 was only from a study of the early stages in ordinary budding 



