MORPHOLOGY OF THE MADREPORARIA. 87 



place, it is seen that the second cycle entosepta, which are to 

 become the permanent second cycle of the adult corallite, arise 

 as independent formations, though later they fuse with the septa 

 which constituted the original second cycle, the two series being 

 situated along the same radii. They are to be regarded as alto- 

 gether new formations which replace the original second cycle 

 exosepta ; the fact that they fuse with the latter in their forward 

 growth would seem to be of incidental importance, depending 

 upon the fact that they are in the same radii. Secondly, the 

 original second cycle exosepta of Fig. 2 lose their morphological 

 individuality, becoming involved in the new second cycle ento- 

 septa as the latter continue their growth centrally ; they are 

 merely the temporary predecessors of a later permanent cycle. 1 

 As primary second cycle exosepta they do not become included 

 within the entocceles of the second cycle mesenteries, but only 

 as the central continuations of the new second cycle entosepta. 

 The results thus afford definite proof that the exosepta of a 

 former stage do not become the entosepta of a later stage when 

 another series of mesenteries has appeared with the entocceles of 

 which they correspond. It is manifest that such a conclusion could 

 only be established in Siderastrea by actual observation of all the 

 intermediate stages. When the condition represented in Fig. 6 

 has been reached there is no means of determining the actual 

 two-fold origin of the second cycle entosepta. It is such condi- 

 tions which have hitherto been studied, and from these no other 

 explanation than that given by Delage and Herouard and by Gar- 

 diner on page 70 would have been expected. Entosepta through- 

 out would now appear to be new formations, not the continuations 

 of the exosepta of a previous stage, and further, they arise after 

 the mesenteries within the entocceles of which they are situated. 



1 In many corals the original second cycle exosepta appear to continue their inde- 

 pendent growth in situ without losing their identity in the central extension of the 

 entosepta. I believe it will be found that this is the true nature of pali, which are 

 found in some corals as small septum-like plates in front of the larger septa. The fact 

 that pali seem not to occur before the primary cycle of six septa, but only before those 

 of later origin, is what we should expect if this surmise be correct. The primary 

 entosepta have never had exoccelic predecessors, as is the case with the later entosepta. 

 Pali would thus represent the persistent exocoalic predecessors of the entosepta beyond 

 the primary cycle which have not lost their individuality in the later growth of the 

 entosepta. 



