_would show a disappear- 
1898-99. | THE MESENTERIAL FILAMENTS IN ZOANTHUS SOCIATUS. 399 
the column of one of these youngest larvae. Owing to its base having 
been somewhat depressed by contraction this has been cut towards the 
central part of the section. Transverse sections of four mesenteries are 
shown ; the two larger mesenteries are one of the macrodirectives (III) 
and one of those which I have taken to be the first formed (I), and the 
two smaller are those indicated in a, previous paper (1891a, PI.IX, Fig. 
6) as V and VI. 
The larger mesenteries, when traced upwards, are seen to become at- 
tached to the stomatodzum, while the smaller ones are imperfect. The 
epithelium which represents the glandular streak seems to be continuous 
above with the ectoderm of the stomatodzeum in the cases of the perfect 
mesenteries, though close examination shows some slight differences: 
in the two epithelia. In the cases of the imperfect mesenteries such a 
continuity is out of the question, and there is not the slightest indication 
of a band of ectoderm extending up the outer wall of the stomatodzum, 
across the under surface of the disk and thence down the free side of 
the mesentery, by which a connection between the glandular streak and 
the stomatodeum might be accomplished. The glandular streak epi- 
thelium can be traced upwards upon the imperfect mesenteries to a level 
a little above the lower edge of the stomatodeum, where it fades out, 
the free edges of the mesenteries being occupied from that point up- 
wards by cells of exactly the same nature as those covering their sur- 
faces. That there may have been in an earlier stage some continuity 
between the stomatodzal ectoderm and the glandular streaks of the im- 
perfect mesenteries is possible ; in my youngest embryos there are, how- 
ever, no signs of any such continuity. 
In the adult condition, 
mesenteries V and VI 
have no filaments (VI 
has in  macrocnemic 
forms),and one might ex- 
pect that older embryos 
ance or diminution of 
the filaments of the mes- 
enteries.- In Fig. 11 is 
represented a part of a 
section through a some- 
what older larva,in which 
the number of mesenter- 
Fic. 11.—Transverse section through a portion of the column of a 
1es still remains at twelve. zoanthid embryo somewhat older than that from which Fig.rois taken, 
