ANATOMY OF THE MADREPORARIAN CORAL FUNGIA. 305 



comparable with the mesenterial filaments, of which thev 

 appear to be a continuation. The lower free edge of the me- 

 sentery appears to be prolonged into a long lamellar offset, 

 which is much plicated, and surrounded along its free edge 

 with the thickening which forms the main body of the acon- 

 tium. This thickening has a similar histological structure to 

 that of a mesenterial filament, differing from it only in the 

 larger size of the epithelial cells of which it is composed, in the 

 abundance of nematocysts, and the corresponding poverty of 

 gland-cells. Fowler describes acontia of similar structure in 

 Flabellum patagonichum, and states that they are pro- 

 truded through cinclides in the peristome (9, p. 14). Although 

 I handled some hundreds of living Fungia I never saw the 

 acontia protruded, either through the cinclides or through the 

 mouth, but in some species of Mseandrina, acontia of exactly 

 similar structure to those above described were protruded 

 through large cinclides on the peristome when the animal was 

 irritated. 



According to Gosse (11) and the Hertwigs the acontia in 

 Sagartia have the form of bunches of long filaments developed 

 at the lower free edge of each mesentery, each filament being 

 ribbon shaped, with one of its borders much thickened. Such 

 acontia are protruded through cinclides in the body wall. The 

 acontia observed by Fowler and myself are protruded in Fla- 

 bellum and Mseandrina through cinclides in the peristome, and 

 appear to be more simple in structure, consisting of a much 

 plicated off-set or prolongation of the lower free border of the 

 mesentery, the edge of which is thickened in continuation with 

 the thickening which forms the mesenterial filament above, 



of tbe mesentery which are in the form of a bunch of filaraeuts. I have fol- 

 lowed Fowler in extending the name to that mass of contorted filaments, 

 which is generally known as the contorted mesenterial filaments. This I have 

 done because (1) they differ in histological detail from the filament on the 

 upper part of the mesentery in exactly the same manner that Gosse's acontia 

 differ. (2) They may be protruded through cinclides. (3) They are clearly 

 a less differentiated condition of Gosse's acontia, but not morphologically 

 distinct from them. To those who adhere to Gosse's original definition, the 

 name as I use it in the text, would be incorrect. 



