ZooL.— Vol. II.] ROBERTSON-ENTOPROCTA. 327 



spines extends to the base of the calyx, where another rib 

 occurs which extends around it to the ventral side (fig. i, 

 has. r.) . 



The Ventral Region. — Perhaps the most striking feature 

 of the calyx is the extreme obliquity of the tentacular disc. 

 This is so great that a point at the base of the tentacles on 

 the dorsal side forms the summit of the calyx (figs. 1-2, 

 sum.), and thus the whole tentacular region is on the ven- 

 tral side. This, in the retracted condition, is a somewhat 

 flattened oval disc which is bounded dorsally by the tentac- 

 ular rib spoken of. In the center, an oval opening may be 

 seen, around which the edge of the lophophore is gathered 

 in strong folds by the sphincter muscle (figs, i and 2, 

 loph.f.). Figure 3 is a para-sagittal section of the calyx 

 and shows the sphincter muscle in cross-section {sph. loph.) 

 and the fold of the lophophore projecting beyond it 

 {lofh.f.). 



The cuticle on the ventral side is very thin, and is thrown 

 into a number of transverse wrinkles or folds during con- 

 traction (fig. 3, etc.). Under the cuticle is a densely stain- 

 ing layer of ectodermal cells (fig. 3, ec.'). Between the 

 ectoderm and the oesophagus is found the somatic portion 

 of the muscle which characterizes this form, and which, 

 since it is to so large an extent continuous in both calyx 

 and stalk, is designated as the ventral ?nuscle (fig. 2, v. 

 tmis.) . 



The Musculattcre. — There are four systems of muscles in 

 the calyx: viz., the somatic portion of the ventral muscle, 

 the sphincter muscle, the tentacular muscles, and the mus- 

 cles of the intestine. 



The Ventral Muscle. — This muscle consists of a large 

 number of bundles, each composed of a number of fibers. 

 Scattered through it and at points of attachment are numer- 

 ous large nuclei. Distally, it is attached to the body-wall 

 of the calyx at the base of the tentacles. It extends in a lon- 

 gitudinal direction through calyx and stalk, and is attached 

 proximally to the base of the stolon. The continuity of 



