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 the prostom ium. 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 Rhabdoccela. Short, retractile, marginal, or 

 dorsal tentacles may project (Proceros, Stylochus, 

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

 Im-tli'-m-d and crumpled as pseudo-tentaculae. In 

 Nemertinea, a special proboscis exists in front of the 

 mouth, an e\vrsil)lt- muscular sac (l*"ig. 21,5) 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 ih<- 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} 9 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 (Microstomidae, 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 (Dendroccela). Some Nemerteans 

 have a body cavity around the stomach (which is held 



