Part I1.—Stichodactyline and Zounthee. 189 
supporting it become deeper and deeper to give increased area for its support, 
until they may ultimately unite at their free edges, the muscle thus passing from 
the endodermal to the mesogleeal stage. 
In P. Swifti’, where the general endodermal musculature and the sphincter 
are comparatively well developed, small portions of the latter do actually appear 
to become cut off from the endoderm and become wholly included within the 
mesoglcea (1898, pl. xx., fig. 5), The mesoglceal bays are, however, so deep as to 
suggest the possibility that the appearance of included muscle fibres may be 
merely a result of the direction in which the section is taken. Such would be the 
case if the depressions were deep and oblique to the plane of the section. The 
endodermal muscle is, of course, mesoglceal at the origin of a mesentery in the 
column- wall. 
Concerning the sphincter of P. dichroicus, Haddon and Shackleton (1891 a, 
p- 699) remark:—‘‘Near the upper extremity (in contracted specimens), it 
appears to become embedded in the mesoglcea, a few simple cavities being visible 
in our sections.” We thus possess in the genus, indications, at any rate, of how 
the actual transference from an endodermal to a mesogloeal muscle is effected 
(cf. Haddon, 1898, p. 432). 
The musculature is everywhere very feeble in P. separatus, and the sphincter 
certainly remains entirely endodermal. The polyps of P. monostichus are only 
about half the size of the former; and such a muscular weakness is indicated in 
all the organs that, independently of the interference of the incrustations, the 
sphineter would probably be difficult of recognition. 
Two of the four Antillean species of Parazoanthus which I have examined, 
exhibit in their mesenterial filaments a simpler condition than that characteristic 
of other Zoanthids. 
The structure of the upper part of the Zoanthean filament is well known. It 
is trifid or V-shaped in transverse section. A middle apical portion of ciliated 
supporting cells, granular gland cells, and nematocysts, constitutes the glandular 
streak, Driisenstreif, or Nesseldriisenstreif ; the outer tayer of the two lateral com- 
ponents consists entirely of narrow, ciliated, supporting cells, and forms the ciliated 
streak or Flimmerstreif. Coming between the Flimmerstreif and Driisenstrief 
on each side is a tissue more nearly resembling the ordinary endoderm, and 
described by Professor von Heider (1895, p. 127 and fig. 16), as the ‘‘ Entoderm- 
wucherung.” I do not, however, regard it as homologous with the thickening of 
the mesenterial endoderm immediately behind the filament in its simple form as 
von Heider appears to (cf. his fig. 28). 
Though differing in form the Zoanthean filament accords in histological detail 
with that of most other Actiniaria; the ‘‘ Entodermwucherung,” corresponding 
with what I have termed the “intermediate streak.” 
TRANS, ROY. DUB. SOC., N.S. VOL, VII., PART VI. 2h 
