me 
a 
1898-99. | THE MESENTERIAL FILAMENTS IN ZOANTHUS SOCIATUS. 393 
greater part of the surface, at the attached edge appearing to dip under 
the less specialized epithelium. On the other lamella they are arranged 
in groups, separated by patches of the less specialized epithelium, 
beneath which some of the groups, indeed, appear to lie. This latter 
arrangement is, however, merely an apparent one, and due partly to the 
contraction of the tissues, and partly to the obliquity of the section of 
this lamella ; all the groups are really at the surface in an expanded fila- 
ment. The arrangement in groups, however, is a normal characteristic, 
whose significance will be more readily understood from longitudinal sec- 
tions, and the difference on the two sides of Fig. 2A is due to a slight 
difference in the plane on which the section passes through the two 
lamella, one of which is probably slightly curved. 
In 2B a section higher up, at the level indicated by AA in Fig. 1, 
is figured. It cuts the median portion of the filament longitudinally 
and shows clearly its histological continuity, and, it may be said, its his- 
tological identity with the stomatodzal ectoderm. The structure of the 
epithelium of the lamella is the same as in 2A. 
In Fig. 3 the section no longer cuts 
the median portion of the filament 
but takes the wings twice nearly trans- 
versely and the intermediate portion, 
near the line of attachment of the 
wings to the edge of the mesentery, 
practically longitudinally. It is at the 
level indicated in Fig. 1 by CC, the 
edge of the region of attachment of 
the wings to the edge of the mesentery 
being indicated in this figure by the 
dotted line. In this section one sees 
the ciliated areas dividing the less 
specialized, or, as it may be termed the 
intermediate epithelium into a number 
of bands, a depression between each ~¢- 
of these leading down to a group of =] 
ciliated cells, it being plainly evident 
that these latter do not reach the sur- 
face merely owing to the state of con- 
traction of the tissues. 
i | ie: In Fig. 4 the section passes along 
Fic. 3 —Section of the line indicated by DD in Fig. 
Fic. 4.-Section through 
the ciliated band at the i; that is above, the line of attach- the ciliated bands at the 
level indicated in Fig. level indicated in Fig. 1 
r by CC. ment of the lamella tothe mesentery. py pp. 
