OBSERVATIONS OX FERSH-WATER POLYZOA. 113 



where the fibres were mechaiii<'a11y torn away leaviii^i!,- the shealh 

 uninjared. 



In the nuisciilar layer oî tlie alimentary canal, (jiily transverse 

 fibres are well developed, and the longitudinal fibres, if ever there be 

 any, are very scanty. The layer becomes thicker as we approach the 

 blind end of the stomach. The musculature in (juestion [)erfjrms 

 peristaltic movements, periodically on the (esophageal and fairly 

 constantly on the gastric wall. The ])lii]d end of the latter is subject 

 to strono-er constrictii-ns in accui-dance with the thickened muscle- 

 layer cf this part. The peristaltic movement of the gastric wall helps 

 not only to move about the contents ofthat organ, but also to setid 

 the residue into the intestine. The muscular fibres of the intestinad 

 wall are especially well developed near the anal opening ; they serve 

 to discharge the excrements out of the l)ody and to keep the anus 

 tightly closed. At the point v\diere the blind end of the stomacli joins 

 the funiculus, there is no muscular layer (fig. oo, PI, XIX). 



The muscular laver of the endocyst has already been treated 

 under the body-wall. The outer ring fibres are especially well 

 developed around the orifice oî the cœnœcial branches and f)rm a sort 

 of sphincter to close the opening produced when the polypides re- 

 tract. When the polyjâde is extended, the cœnœcial branch becomes 

 slender by the contraction of the ring fibres, but apparently it is not 

 by their agency that the polypides are pushed out, for tiiis pr(jcess 

 takes place even in a cœnœcial branch witii its wall cut open, so that 

 the fiuid contained can transmit no pressure upon the in\'aginated 

 polypide. 



The muscles that move the epistome remain in a very primitive 

 state of development, coiisisting of hjosely distributed fibres which, 

 as already mentioned, are mere elongated cells with t lie nucleus at 

 the ufiddle. They tra\erse the cavity of the epistome, joining its 



