304 GILBERT C. BOURNE. 



according to their position^ either to the aboral body wall, or 

 to thickened lines of the mesogloea of the skeletotrophic invest- 

 ment shortly to be described. In sections these ligaments 

 may be seen as thickenings of the tissue surrounding each in- 

 tersynapticular passage, more rarely as complete partitions 

 dividing such a chamber in two. The endoderm covering each 

 face of the mesentery becomes continuous, where the latter is 

 divided by the synapticulum, with the endoderm of the skeleto- 

 trophic investment. The theca being perforate in all but its 

 most central portions, the ligaments of the mesenteries pass 

 through the perforations and are continued outside the theca, 

 to be fastened to the aboral body wall (see fig. 15). The theca 

 or aboral surface of Fungia is completely covered with soft 

 tissues which do not closely invest the coral] um, but are 

 separated from the latter by a portion of the ccelenteron. It 

 is important to observe that this extra-thecal portion of the 

 ccelenteron is, partially at least, divided into chambers by mesen- 

 teries in the manner described above. 



The free edges of the primary and secondary mesenteries 

 below their insertion into the stomodseum, and the free edges 

 of the remaining mesenteries in their entire length, are fur- 

 nished with the thickenings known as mesenterial filaments. 

 In the primaries and secondaries the mesenterial filaments are 

 very thick ; their epithelial cells are very long, attenuated, and 

 crowded close together, showing an abundance of deeply- 

 staining nuclei. Nematocysts are scanty ; but I was able to 

 distinguish a number of cells, which seemed to be of the same 

 character as the gland-cells described by the Hertwigs in 

 Actinia and Sagartia (15). In the other mesenteries the fila- 

 ments are not so thick, and gland-cells are less abundant, 

 nematocysts more so ; in other respects their structure re- 

 sembles that of the filaments of the primaries and secondaries. 

 At the lower end of the free border of each mesentery is a 

 bundle of much-coiled filaments, forming the structure known 

 as an acontium.^ These structures in Fungia are strictly 



1 Professor Moseley has pointed out to me that the name acontium is 

 used by Gosse and the Hertwigs to describe only those structures at the base 



