NEMERTEA. 



265 



has muscular walls, and contains a corpasculated fluid; it contains 

 a closed cavity (rliyncliocoeloni), and its epithelioid lining is 

 continuous anteriorly with that covering the outer side (in the 

 retracted state) of the proboscis, i.e. with the epithelium on that 

 surface of the retracted proboscis which is in contact with the 

 proboscis-sheath fluid. The proboscis and its sheath may therefore 



FIG. 220. A young Pdagonemcrtes Rollestoni, dorsal view (after Hubrecht, from Perrier). P pro- 

 boscis ; (f sheath of proboscis ; I intestine ; D diverticula of intestine ; C cerebral ganglia ; 

 N lateral nerve cords ; V lateral vessels ; ovaries : A amis ; m longitudinal muscles ; 

 t transverse muscles. 



be compared to the finger of a glove, of which the free end is 

 pulled in upon the portion next the hand, the pulling in being 

 effected by a string attached to the inner side of the tip of the 

 glove, and lying inside the finger. From the above description it 

 will also be clear that the epithelium lining the inner surface of the 

 retracted proboscis is^continuous with the surface ectoderm of the 



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