OLTGOTREMA PSAMMITES. 257 



The edges of fclie stigmata are clothed with a ciliated epi- 

 thelium so similar to that of other Ascidians as to require no 

 description. 



The CEsophagus and. Stomach. 



The walls of both the oesophagus and stomach are longitu- 

 dinally folded, but as the epithelium is more or less detached 

 from the walls of the gut it is difficult to say how far the 

 folds shown in figs. 12, 13, and 14 are natural, and how far 

 they are due to conti*action in spirit. The corresponding 

 folds of the endoplei'ome in the stomach (fig. 14) indicate that 

 in this region, at any rate, they are natural. The anterior 

 section of the oesophagus is lined by a glandular epithelium 

 exactly similar to that of the oesophageal groove; towards 

 its posterior end the glandular cells increase in size and 

 their nuclei become more rounded, and they g-radually pass, 

 without any definite line of demarcation, into the much 

 longer and. larger epithelial cells of the stomach, shown in 

 fig. 27. The epithelium of the stomach is composed, of very 

 large wedge-shaped cells, with narrower basal and broader 

 outer ends. The nucleus is situated near the basal end of 

 each cell, is spherical, and has a distinct nucleolus. The 

 cytoplasm of the nai-rower basal end is dense and finely 

 granular, that of the broad outer end (i.e. the end turned 

 towards the lumen of the gut) is vacuolated, and in most 

 cases contains accretions of yellowish crystals, which are 

 apparently products of digestion ; but as I was unable to 

 apply any micro-chemical tests to my sections I cannot say 

 whether they ai'C nitrogenous or not. 



The form and relative size and extent of stomach and 

 oesophagus are clearly shown in the diagram, fig. 34. 

 The stomach exhibits a sharp ventral flexure, and is therefore 

 U-shaped; the walls of the distal limb are not longitudinally 

 folded, but are lined by the same kind of epithelium as those 

 of the proximal limb. 



The oesophagus of my specimen was empty, but both limbs 



VOL. 47, PAKf 2. NEW SERIES. R 



