596 ANATOMY OF NEOHEI.IA PORCELLAXA (mOSELEY). 



by Bourne (4) in Mussa and called by him " desmocytes." Owing to their minute 

 size in this foi-m I have not been able to confirm Bourne's results as regards other 

 details of these interesting structures. 



Mesenterial filaments as stated above occur only on the primary and secondary 

 mesenteries. In transverse section they are seen to be three lobed. Gland cells are 

 numerous, but no nematocysts have been seen on them. In this respect Neohelia 

 agrees with Flahellum patagonichum, of which Fowler (10, p. 16) says: 



" Nematocysts do not occur apparently in- the true mesenterial filament, but only 

 on that portion of it which is continued on to the contorted lamellae, which I regard, 

 in part at least, as equivalent to the acontia of Actiniae." 



Acontia. The lower portion of the coelenteron is occupied by numerous groups 

 of structures coiled together. In some cases they are protruded through the anterior 

 body wall outside the crown of tentacles. In section they are then seen to be more 

 or less rounded structures occurring in groups of four or five arising from a common 

 stem which is given off from the free edge of a mesenter}^ (Figs. 8 and 3). These 

 acontia, for such I believe them to be, are armed with numerous large nematocysts 

 (Fig. 7) which, when exploded, are seen to be provided with a formidable spirally- 

 barbed thread of great length. Similar nematocysts in an uuexploded condition were 

 observed on the epithelium bordering the apertures in the tubular wall of the colony. 

 Length of unesploded nematocyst "038 mm. Gland cells are numerous round the 

 periphery of the acontia, the internal portion of an acontium is made up of spindle- 

 shaped interstitial cells, developing gland cells and nematocysts. The stem supporting 

 the acontium is composed of an axis of mesogloea which extends into and branches 

 in the acontium in a manner similar to that described by Bourne in acontium of 

 Fungia (3). The mesogloeal axis is covered by a single layer of eudodermal cells. 



Of Flahellum patagonichum (Moseley) Fowler says: "What Moseley has termed 'the 

 contorted mesenterial filaments,' a mass of coils lying on the side of the mesenteries, 

 appear to me after careful investigation to be, in part at least, organs corresponding 

 to the acontia of Actineae, namely, long lamellar offshoots of the fi-ee edge of the 

 mesentery with one edge thickened to correspond to the mesenterial filament, and 

 charged with large nematocysts. They protrude in some instances through definite 

 openings in the mouth disc. Their exact origin fi-om, and relation to the mesenteries 

 I have not been able to detect owing to the brittle condition of the specimens." 



There seems to me to be little doubu that these structures described by Fowler 

 in Flahellum are very similar to the acontia described by Bourne in Fungia, and to 

 those occurring in Neohelia. In the latter, however, I have observed no instance in 

 which the acontia are thrust through apertures in the mouth disc, in every case, 

 which I have examined, they are everted through the anterior body-wall outside the 

 crown of tentacles. 



