232 CEYLON PEARL OYSTER REPORT. 



which two are directives, are well developed and reach the stomodseum ; they embrace 

 the primary endosepta, the latter being tolerably well developed as narrow, ridge-like 

 projections in the calicle, but with branched peripheral ends passing into the network 

 of trabecular forming the coenenchyme. Alternating with the endosepta are six 

 exosepta of approximately the same size, whose peripheral ends bifurcate and enclose 

 chambers in which are the mesenterial pairs of the second cycle. These secondary 

 mesenteries are unequally developed, but not, as far as I could determine, according 

 to any regular sequence. Each pair embraces an endoseptum, which in some cases is 

 very rudimentary, but in other cases has grown centipetally and has united with the 

 inner limb of the Y-shaped exoseptum (fig. V). Thus we see that in the bud the 



Fig. V. Semi-diagrammatic section through a young bud of Dendrophyllia gracilis. 1, 2, the primary and 



secondary cycles of endosepta embraced by the corresponding mesenterial pairs. 1>, l>, the two pairs 

 of directive mesenteries, ex, an exoseptum with forked peripheral ends, within which a pair of 

 secondary mesenteries enclosing a secondary endoseptum is developed. /', t 2 , tentacles of the first 

 and second cycles corresponding to the endosepta. 



secondary mesenteries, and the endosepta embraced by them, are formed between 

 the bifurcated outer ends of the exosepta, and show the same relations to the latter 

 that the tertiary endosepta show in the adult. This is a clear proof of the nature ol 

 the septal sequence. 



