63 
Further, the two arms of the lophophore will represent the 
labial tentacles of a Lamellibraneh ; and since that portion of 
the endocyst which forms the tentacular sheath in the 
retracted state of the polypide is apparently continuous with 
the posterior edge of the mantle, there can be no difficulty in 
finding, in the ccrncecium of a Polyzoon the representative 
of the siphon of a Lamellibraneh. 
It should also be noticed that the whole polypide of Rhab- 
doplcura is remarkably compressed from side to side, a fact 
which further bears out the views here maintained of its 
relations — views, however, which are in no "way inconsistent 
with the obvious relations of the Polyzoa to the Tunicala. 
The following diagrammatic figures will facilitate a compre- 
hension of the relations here attempted to be proved between 
a Polyzoon and a Lamellibraneh. 
Fig. 1. — Diagrammatic Section of a Lamellibranchiate Mollusc. 
a, stomach ; l, intestine; b' anus; c, labial pulp ; d, ventral edge of mantle ; 
d' dorsal edge of mantle; e, siphon ; f, pedal ganglion ; g, cephalic 
ganglion; A, parietal splanchnic ganglion; i, heart; k, posterior re- 
tractor muscle ; k' anterior retractor muscle. 
Fig. 2. — Diagrammatic Section of a Dud of Rhabdopleura. 
a, stomach; b, intestine; 6', anus; e, lophophore ; d, ventral or open edge of 
mantle ; d' dorsal or closed edge of mantle ; e, coenoccium ; e' reflected 
portion of endocyst forming tentacular sheath. 
