i62 ARCHICCELOMATA. 



collar pores) lead out from the collar at its hind end. 

 In the front region of the trunk, opening dorso-laterally 

 into a long dorsal groove, there are two rows of small 

 slits which open downwards into the alimentary canal. 

 They are numerous and are known as the pharyngeal 

 clefts. Lying outside the pharyngeal clefts, and also con- 

 tinued backwards behind them, are two rows of genital 

 pores. 



Fig. 94. — Semi-Diagrammatic View of Balanoglossus 

 FROM THE' Dorsal Surface. 



Proboscis. 



Anus. 

 Collar. 



Hepatic Glands. 



The ectoderm consists of a simple ciliated epithelium 

 with unicellular mucous glands. 



The mouth leads into an elongated pharynx. Tlie 

 extreme anterior wall of this pharynx is pushed forwards 

 Alimentarv ^"^^ ^^ proboscis as a diverticulum, the sub- 

 neural gland.^ The epithelial cells, forming 

 the wall of this organ and that of the anterior part of 

 the pharynx, are metamorphosed into chordoid tissue (see 

 Chapter XXIV.). Their protoplasm is almost entirely re- 

 placed by vacuoles with walls and scattered nuclei, amongst 

 which there may be small glands. This structure converts 



* This organ is also known as the " notochord " or " stomochord." 



