CLASSIFICATION OF ACTINIARIA 575 
Exoconn.—the space between two pairs of mesenteries. 
Fossx.—Some anemones have the margin of the body 
raised into a distinct rim or parapet, outside the bases of 
the tentacles ; the circular groove between this parapet and 
the tentacle-bases is known as a fosse. 
MacrocneEME.—A typical macrocneme is a well-developed 
mesentery which joins the actinopharynx as well as the body- 
wall, has a strong and usually circumscribed retractor muscle, 
a gonad, and a mesenterial filament. There are sometimes 
variations in detail from this general plan. 
MErtTACNEME.—Any mesentery formed after the earliest 
eight mesenteries to appear (protocnemes). 
MicrocNEME.—lypically a narrow mesentery which 
does not join the actinopharynx, has little or no muscle beyond 
a ‘parietal muscle ’—no retractor therefore—no gonad, and 
no filament. Variations from this typical scheme are found, 
however. 
NEMATOSPHERE.—A tentacle which has become con- 
verted into a short structure rounded at the end, or into a 
practically sessile sphere, and the ectoderm of at least part of 
which is crowded with nematocysts. 
Parr of mesenteries. See foot-note on previous page. 
Prerrect Mrsentery.—In a form where there are 
graded cycles of mesenteries (i.e. no division of the mesenteries 
into macro- and microcnemes), any mesentery which joins 
the actinopharynx as well as being inserted into body-wall 
and oral disc, is termed ‘ perfect’. In a form where there 
are macro- and microcnemes, the former are of course ‘ perfect, ’ 
as part of their macrocnemic nature ; but in some cases some 
of the microcnemes may join the actinopharynx though 
otherwise more or less rudimentary. They are then technically 
‘ perfect ’ mesenteries, but are by no means macrocnemes. 
In the forms with graded cycles, the perfect mesenteries have 
filaments and retractors, but not always gonads, which in 
such forms may appear on the ‘ imperfect ’ mesenteries only. 
In such forms the older imperfect mesenteries, at least, may 
have retractor, gonad, and filament, so that they are not 
Qq2 
