Part I1,—Stichodactyline and Zoanthee. 185 
musculature. Distally the mesenterial endoderm closely resembles that of the 
column-wall, but contains a greater number of the glandular cells, with highly 
refractive contents. Proximally it becomes swollen, and contains many granular 
particles of various sizes, while elongated gland-cells are still more numerous. 
The parieto-basilar muscles are developed for some distance along each face of 
the mesentery, and are continued a short way on to the column-wall. There is 
no trace of any mesoglceal folding or pennon. 
Both cycles of perfect mesenteries remain connected as far as the inner ter- 
mination of the stomodzal-wall. I have not been able to determine any definite 
order in which they become free, but the directives at one end remain united 
further than the opposite pair, the laterals being the first to cease their connexion. 
The imperfect mesenteries project for some distance within the ccelenteron. 
In section they are almost as broad as the complete mesenteries, and the mesoglea 
terminates in numerous processes, each surrounded by a muscular layer, which, 
so far as it extends, is as strongly developed as on the first cycle. All the 
endoceelic and exoccelic spaces are practically equal, and the mesenteries by no 
means fill the ccelenteric space. 
The terminal edge of the stomodeeum is reflected as a whole, so that in sections 
through this region the wall is double im all its three layers (Pl. xm, fig. 4). 
The reflected ectoderm passes for some little distance outwardly along each face 
of the mesenteries, and appears in perfect continuity with the tissues forming the 
mesenterial filaments. At first the filaments are very irregular and narrow in 
outline, forming only a slightly rounded termination to the mesenteries; they are, 
however, histologically very distinct from the rest of the mesenterial epithelium. 
Lower they become more characteristic, and are either rounded or cordate in 
section (Pl. xv., fig. 3). 
The mesenterial filaments are remarkable in that only the middle terminal 
lobe, the glandular streak or Nesseldriisenstreif, is ever developed ; the lateral 
lobes, bearing the ciliated streak or Flimmerstreifen, so characteristic of most 
Actiniaria, are never produced. 
A little below the aboral termination of the stomodzeum the mesenterial 
endoderm is considerably swollen immediately behind the filament, so as to produce 
in section somewhat the appearance of a trilobed filament ; but these enlargements 
cannot be regarded as at all comparable with the lateral lobes of the more usual 
Actinian filament. Except in length of the constituent cells they differ in no 
important respect from the remainder of the mesenterial epithelium into which 
they often graduate insensibly, while the distinctly lobed character is not presented 
by all the mesenteries. Further, the mesoglceal axis never sends a branch into 
these swellings for the support of the cells, as is the case where the Flimmerstreifen 
are developed. Such a filament is characteristic of the Madreporaria, and 
