30 PERCY SLADEN TRUST EXPEDITION 



commonly form coiled masses, the acontia" (52, p. 123). Duerden could see no 

 " cinclides " in the living coral polyps he examined, but observed that the filaments with 

 the contorted edges of the mesenteries could be protruded through the mouth or through 

 temporary openings on any part of the column-v?all or oral-disc, but that such extensions 

 were different from the acontia of Sagartia. 



The term " acontia " was first applied by Gosse to the threads in the Sagartidce, 

 which he found protruded through special openings (which he named " cinclides "), but 

 gave no structural characterization of the threads. They were re-described by the 

 Hertwigs, but the exact relation between their acontia and " mesenterialfaden " (66, 

 PL 8, figs. 10 and 12) is not evident. Faurot in 1895 remarked that an acontium 

 has "a peu pres la meme structure histologique que I'enteroide," and that it was for 

 augmenting the digestive surface of the mesenteries and "non d'etre utilises uniquement 

 comme arme defensive" (40, p. 53). In 1897 van Beneden defined them as arising from 

 the mesenteries between the terminations of the mesenterial filaments and the aboral ends 

 of the polyps, and gave as the essential difference between the two structures that while 

 the epithelia of acontia were endodermal, those of the filaments were ectodermal, 

 being continuations of the stomodeeal ectoderm. According to Duerden, " acontia (in the 

 Sagartidse) are thread-like structures, which are but feebly attached to the mesenteries, 

 and pass through permanent apertures (cinclides) in the column wall of the polyps, or 

 through the mouth, the mesenteries in no ways following. If not wholly liberated from 

 the polyp, the acontium can be indrawn. The extruded filaments of corals, on the other 

 hand, still retain their normal position along the contorted edge of the mesentery, and 

 a portion of the latter passes out along with them. The function of both is probably the 

 same, as in each case the organs are strongly charged with nematocysts, and less so with 

 gland cells" (32, p. 476). 



Is the name "acontia," then, to be restricted to thread-like structures, which are 

 attached by one extremity to mesenteries below the terminations of the filaments and 

 endodermal in structure, and is their presence always correlated with that of " cinclides"? 

 In my coral polyps I have not satisfactorily investigated if among the convolutions of the 

 mesenterial filaments, which are so often protruded into the peristome, there are any 

 threads comparable to the acontia of Sagartidse. 



Reproductive Organs. Mature ova have been seen in many of the polyps 

 examined (PL 1, fig. 10, PL 3, fig. 29, and PL 5, fig. 49). They are carried by all the 

 mesenteries or by the primaries only, forming one to five or six longitudinal rows. The 

 ripe ovum is large, varying in size in the different species, enclosed in a thin vitelline 

 membrane ; its cytoplasm is highly vacuolated, the vacuoles being somewhat small and 

 round and the nucleus large, stained pink, excentrically situated, with a dark-stained 

 nucleolus on one side. It lies in the mesogleea usually on its exocoelic side ; the mesoglaea 

 surrounding it is narrowed to a thin membrane, while the mesenterial endoderm over it is 

 usually swollen and granular, perhaps for nutritive purposes. 



Surrounding the large ova are frequently seen some small cells which, for reasons 

 given below, I take to be germ-cells. These lie in the mesoglaea or in the surrounding 

 mesenterial endoderm, each consisting of a large spherical nucleus — similar to those of the 



