3 G. HERBEET FOWLER. 



one case as a tendency to a longer course, and to the more 

 complete development of the filament ; in the other as the 

 peculiar modification described above ; and in both types two 

 of these six have of all the longest course^ and are, so far as I 

 have observed, the only ones that bear reproductive organs. 



Neither type is confined to certain areas of the branch, but 

 both appear to be irregularly distributed. 



Tentacles are not recognisable in ray specimens, but it is 

 probable that in the living animal they occur as slight evagina- 

 tions of the chambers, and have shrunk under the action of the 

 alcohol in which the polyps were killed. 



Muscles are obviously present on the mesoderm lamella of 

 the mesenteries, but owing to their minute size it is impossible 

 to detect how they are arranged. I see no reason to doubt 

 that they agree with Actinia. So far as it is possible to judge 

 without this clue, the septa are entoccelic. 



c. Histology. — There is but little to be said under this head, 



except as regards the modified mesentery, an almost transverse 



section of which is represented in fig. 9. The state of the 



specimens did not allow of an exhaustive study of cell structure, 



but those cells, the elongation of which causes the peculiar 



swelling on both surfaces of the mesentery, are apparently 



simply lengthened, much vacuolated, and amoeboid at their free 



ends. No food particles were detected in them, or indeed in 



any other part, but many zooxanthellse are embedded amongst 



them. These cells pass gradually into the ordinary endoderm, 



and their appearance suggests strongly that their condition is 



merely an exaggeration of that of the '^ Flimmerstreifen " of 



the brothers Hertwig, i. e. of the two lateral lobes of the 



mesenterial filament. 



In a recent paper (5) Dr. Wilson has suggested that these 

 lateral lobes are ectodermic in origin, circulatory in function, 

 and homologous with the "ectodermic bands ^^ described by 

 him on the axial mesenteries of certain Alcyonaria. I may 

 here state that, so far as histological evidence from the adult 

 is valuable, it points, in all the Madreporaria that I have yet 

 examined, distinctly in the other direction. The central 



