536 T. A. STEPHENSON 
each. The contrast is differently brought out in Text-fig. 14, 
p and Fr, which represent two sectors of the oral disc of two 
forms. One of these (p) has the ordinary arrangement of 
tentacles in alternating cycles, one to each mesenterial space ; 
the other (F) is from an Antheopsis, and shows two of the 
long radial rows situated over endocoels (which are shaded) 
and also the arrangement of the marginal tentacles, one or 
two to each endocoel, one to each exocoel (exocoels are not 
shaded). 
Text-Fic. 15. 
Diagrams of three types of tentacular arrangement. In each diagram 
three cycles of mesenteries are shown, with their retractor 
muscles as black thickening; endocoelic tentacles black, exo- 
coelic white. In A there are cycles of tentacles, one tentacle 
only to each exocoel and endocoel. In B there are radial rows 
on the endocoels, but only one tentacle per exocoel (e. g. Stoichac- 
tidae). In c the exocoels as well as the endocoels have more 
than one tentacle (e. g. Homostichanthidae). 
Stichodactylines have a definite base (occasionally reduced 
and half like a physa). Cinclides are recorded in at least one 
case (see p. 501). There is a complete absence of acontia and 
mesogloeal sphincters, and almost complete absence of vesicles 
(there is one case of somewhat vesicular verrucae). The 
musculature is always reasonably well developed, at least in 
the mesenteries. ‘There is either no approach to a division of 
the mesenteries into macro- and microcnemes, or if there is, 
there are at least twelve pairs of the macrocnemes; in the 
first case there are usually numerous perfect mesenteries. 
