220 



CEYLON PEARL OYSTER REPORT. 



ent.m 



Fig. III. Semi-diagrammatic representation of six successive horizontal sections through the same sextant 

 of Heterocyathus cequicostatus. The corallum is shaded with dots; the mesogloea is represented by a 

 black line, the endoderm by a contour line following the mesogloea; the ectoderm is blocked. 

 A passes through the exsert portion of the septa, B through the mouth, C and D are sections about 

 0-25 millim. apart and below the mouth ; the interseptal loculi in these sections are not reduced by 

 the formation of secondary calcareous deposit or " stereoplasm." In E a considerable amount of 

 stereoplasm bas been deposited in the loculi adjacent to the primary endoseptum. In F all the loculi 

 are reduced by the deposit of stereoplasm and the mesenteries contain ova. ent.l., ent.U., endosepta 

 of the first and third cycles ; portions of the second-cycle endosepta may be seen at the edges of each 

 sextant, ex., exosepta. fil., band-like primary mesenterial filaments, (jr., groove leading from the 

 mouth to one of the primary mesenterial filaments, m.f., coiled mesenterial filaments. /.', t.", /.'", 

 introverted tentacles of three cycles doubled over the corresponding endosepta. col., columella. 



columellar upgrowths. There is not, in fact, room for a stomodseum in the contracted 

 polyp. 



The Mesenteries. These are of the normal Actinian character and are 



