156 Introduction to Animal Morphology. 



The persistent embryonic mouth (homologous with 

 the anus of some higher forms) is either anterior or 

 abdominal, surrounded by radiating and sometimes 

 circular muscle-fibres, and may be trumpet-like, 

 plicated in some land forms. The part of the body in 

 front of it is XhQprostoiniiun. The pharynx is muscular 

 (except in Schizostomum), and may be protrusible, 

 with one-celled glands opening therein (Vortex, De- 

 rostomum), or with 2-3-celled (salivary) glands in 

 some Rhabdocoela. Short, retractile, marginal, or 

 dorsal tentacles may project (Proceros, Stylochus, 

 &c.), or the skin of the front of the body may be 

 lengthened and crumpled as pseudo-tentaculae. In 

 Nemertinea, a special proboscis exists in front of the 

 mouth, an eversible muscular sac (Fig. 21,^) sometimes 

 as long as the body, or longer ; when retracted, it lies, 

 convoluted, in a sheath or short sac, surrounded by a 

 corpuscular fluid, under the dorsal integument and 

 over the intestine ; when protruded (by the action of 

 the circular fibres in its wall), its apex is, in Nemertinea 

 enopla, armed with a strong spine, often surrounded by 

 smaller ones ; a saccular poison gland {c\ placed near 

 the end of the cavity of the protruded proboscis, opens 

 by a duct at the base of the chief spine ; a retractor 

 muscle arising from the body-wall traverses the axis 

 of the proboscis to its tip, and can draw it in. Some 

 Nemerteans (N. anopla) have no spines. 



The stomach may be a simple pouch (Rhabdocoela), 

 with (Microstomidse, Nemertinea) or without an anus,' 

 or it may give off branching, coloured caeca, or the 

 tube may begin to branch at the pharynx ; in these 

 cases it is aproctous (Dendrocoela). Some Nemerteans 

 have a body cavity around the stomach (which is held 



