Or.TOOTIJEMA PSAMMTTRS. 255 



the oesophageal groove. There are also tracts in the branchial 

 sac where it passes into a layer of simple non-flagellated 

 cubical cellsj and these in turn are succeeded by a tract of 

 wedge-shaped^ ciliated cells^ as shown in fig. 18^ c. A short 

 band of these ciliated cells could be traced on the ventral 

 side of the branchial sac, just in front of the branchial slits, 

 and I regard this band as the representative of the endostjle. 

 I cannot be certain of its extent, as the epithelium is largely 

 peeled off in this region and lies in strips in the brancliia 

 sac. A similar band of ciliated epithelium can 1)0 traced on 

 either side of the branchial sac, apparently nearly coinciding 

 with the anterior limits of the right and left peribranchial 

 cavities ; but the condition of the epithelium prevents my 

 saying anything certain on this point. At all events, the 

 lateral bands of ciliated epithelium exist and run from the 

 ventral towards the dorsal surface on either side of the 

 branchial sac. They must therefore be regai'ded as repre- 

 senting the peribranchial grooves. 



At the lips of the cesophageal groove, where the epithelinm 

 is marked with a l)lack line in figs. 9 and 10, there is on either 

 side a band of richly ciliated epithelium, which rnns all along 

 the lips of the groove and passes rather suddenly on their 

 ventral side into the characteristic flagellated epithelium of 

 the branchial sac. These bands of ciliated epithelium are very 

 fiiirly well preserved ; their component cells are represented 

 in fig. 20^ and it is obvious that they differ from the ciliated 

 cells of the endostyle and peribranchial grooves, and belong 

 rather to the category of the oesophageal epithelium. Dorsally 

 these ciliated bands are succeeded by a tract of non-glandular 

 cubical cells, which pass into the glandular epithelium of the 

 oesophageal groove. These ciliated tracts may possibly 

 represent the dorsal lamina. Their function is clearly to 

 direct food into the oesophagus. 



The Branchial Slits. — The branchial sac, as has been 

 described, commences posteriorly as an irregular space in the 

 thickness of the ventral suspensory fold. The thick lateral 

 walls of the snc are honeycombed by a number of irregular 



