390 



Dr. J. E. Duerden on the 



Separation of tlie results of fission by the production of 

 transverse partition walls takes place much more frequently 

 in Favia than in Manicina. On any fully established colony 

 of Favia many so-called polyps possess only one mouth, 

 others two or three, but not often more. After its formation, 

 therefore, a stomodreal system may become entirely separated 

 from the others, provided with its own disk, zone of tentacles, 

 and column wall, as if it were a distinct polyp. A number 

 of these apparent polyps have been sectionized, bat none show 

 any directive mesenteries, and the hexaraeral plan is wholly 

 departed from. Two or three different sizes of mesenterial 

 pairs are represented, but the grouping does not retain the 

 cyclical regularity all the way round. They are simply 

 fragments cut off a larger polyp and do not represent new 

 individuals. 



Fig. 4. 



Arrangement of the mesenteries in a portion of a colony of Maandrina 

 labynnthica. Two complete stomodaeal systems are represented and 

 parts of other two. The septal invaginations at this level are all 

 entocoelic. Partly diagrammatic. 



The close similarity in the polypal systems of adult colonies 

 of Isojyltyllia, Mmandrina, Colpoijhyllia, &c. to those in 

 Manicina and Favia, and the like general arrangement of 

 the mesenteries and septa, would lead one to infer a similar 

 course of development for these fission genera — that is, that 

 all have been derived from the continued growtli and 

 fission of a single primarily hexaraeral polyp. A transverse 

 section through a part of the polypal growtli of Mceandrina is 

 represented in fig. 4 for comparison with the fission-stages in 



