12 G. HERBERT FOWLER. 



in pairs 1 on the normal type. In the diagram (fig. 9) they 

 are numbered in the same manner as those of Madrepora (3) ; 

 the two mesenteries marked 3 and 10 respectively are compa- 

 ratively long, extending to the bottom of the polyp cavity, and 

 possess the thickened edge known as a mesenterial filament ; 

 of the rest, those numbered 1, 5, 8, 12, though generally de- 

 void of a " filamentar 5 ' thickening, are recognisable in trans- 

 verse sections for some distance below the stomatodseum ; 

 while the others, 2, 4, 6, 7, 9, 11, are rudimentary, and are 

 visible only in the highest sections. It is worthy of remark 

 that the six rudimentary mesenteries last mentioned are those 

 which in the one type of polyp of Madrepora Durvillei, 

 are pierced by a special ectodermal canal, and which in the 

 other type of polyp of the same species, and in all the polyps 

 of M. aspera, are distinguished from the remaining six by a 

 greater length and the possession of a filamentar thickening ; 

 in other words, of the total twelve mesenteries the 

 six which in the one form are the best developed 

 are in the other quite rudimentary. 



The histology agrees with that of the normal types. I have 

 found no trace of generative organs in my specimens. 



iii. Summary. — The interesting points in Seriatopora are : 



1. The polyps are Actinian in structure. 



2. The septa when all are present, and the tentacles, are 

 both ectocoelic and entocoelic. 



3. The tentacles are retracted by introversion. 



4. The body wall is supported upon the echinulations of 

 the ccenenchyme. 



5. Of the twelve mesenteries, six (and more especially two 

 of these) are of some length, and six are rudimentary ; but 



1 Professor Moseley (10) states that in Seriatopora and Pocillopora the 

 mesenteries " are not disposed in pairs with regard to the septa ; " and the 

 remark reappears in a misleading form in Professor Martin Duncan's " Re- 

 vision of the Madreporaria " ( f Journ. Linn. Soc. Zool.,' vol. xviii), to the 

 effect that " the genera differ from other Madreporaria in not having their 

 mesenteries arranged in pairs." The original statement was correct because 

 the possibility of ectocoelic septa in a coral had not been demonstrated. 



