Morphology of the Madreporaria. 4G7 



of niucli ninr|ilKiln(rical sif^nificance have been found, notwith- 

 standiiig that tlie external and anatomical details of a lar<^e 

 number of genera and species are now known. It would 

 rather seem that structural complexity within the Madreporaria 

 is lartijeiy confined to the skeleton, where much diversity of 

 form is recognized, the details of which are employed for 

 taxonomic purposes. Tiiough all this skeletal variability 

 must necessarily be correlated witii structural differences 

 in the soft polypal tissues, yet these are modifications of 

 but insignificant morphological value, according to accepted 

 standards. In view of this general conformity to type a 

 j)eculiarity associated with tiie tentacles of certain polyps 

 in three Madreporarian genera seems worthy of notice. 



M. Arm. Krempf *, when studying in 1903 representatives 

 of the genera Seriatopora, Sti/lopho) a,a.ni\ Pocillopora, obtained 

 from the Red Sea, found in certain polyps of each colony a 

 peculiar cellular formation, situated between the mesenteries, 

 and evidently associated with the tentacles. In Seriatopora 

 the peculiarity consists of a single long cord-like organ 

 inserted in the disk over the ventral directive entocoele and 

 hanging down into the polypal cavity; a continuation of the 

 discal mesoglcea accompanies the downgrowth throughout 

 its length and constitutes a kind of skeletal axis. The 

 organ first makes its appearance as a simple papilla of the 

 endoderm, and afterwards increases in length. In Stylophora 

 a similar downgrowth occurs, but a short axial canal is 

 present, lined internally with ectoderm ; inwardly the canal 

 terminates blindly, but externally it opens on to the disk. 

 In Pocillopora the structure is like that of Seriatopora^ but 

 the number of cords is increased to three, the middle one of 

 which occupies the ventral directive entocoele, and the others 

 the exocceles one on each side of the directive entocoele. 



Krenijif comes to the conclusion that the organs are 

 invaginated tentacles which have become considerably 

 modified in size and structure as a result of their unusual 

 position, the modification extending much further in Seriato- 

 pora and PociUopora than in Stylophora. 



While investigating the polyps of various species of 

 Pocdlopoia obtiiined trom the Hawaiian Islands a few indi- 

 viduals presented structures which at once recalled the brief 

 account given by Krempf. The ap|)earance of these in 

 vertical sections is given in figs. 1 and 2, and in transverse 

 sections in figs. 3 to 5. Fig. 1 represents a vertical section 



♦ Krempf, A., " Sur un Point de TAnatomie de quelqiies llexa- 

 coralliiuros,'' Coui})tt'S Keudus, 1!KJ."3. 



