THE STRUCTURE OF XENIA HICKSONI. 251 



most resembles X. umbel lata, Savigny, but it differs from 

 the latter in possessing smaller polyps, with much shorter and 

 stouter pinnules, which do not leave the axis of the tentacle 

 free along its whole length (cf. Klunzinger, 1877, pi. 3, 

 fig. 3a). 



General Anatomy. 



Stomodaeum and Mesenterial Filaments. — In the 

 centre of the oral disc of each polyp there is a funnel-shaped 

 depression about one third of a millimetre in depth leading to 

 the mouth. This depression is formed by partial contraction 

 of the oral disc ; if the polyp were fully expanded this depres- 

 sion would not exist, but the mouth opening would be level 

 with the oral disc. The mouth {Mo.) leads into the stomodseum 

 (St.), which is 1*8 mm. to 2*2 ram. long. The stomodseum is 

 long compared with the length of the free portion of the polyp, 

 and in longitudinal section presents a striking appearance, 

 running down, as it does, so far into the coelenteron. The 

 stomodseum is oval in transverse section, being somewhat 

 flattened from side to side. It has a well-marked ventral 

 groove or siphouoglyph [Si.), the cells of the lower third of 

 which bear long flagella (F.). The groove is not as well 

 marked in the upper as in the lower portion of the stomodseum, 

 and is scarcely discernible at the mouth opening. The 

 columnar epithelial cells forming the siphouoglyph are, as is 

 usual, longer than those of the rest of the stomodseum, and 

 these cells bear very long flagella ('07 mm.), which in some 

 examples extend almost to the centre of the cavity of the 

 stomodseum. The epithelium of the rest of the stomodseum is 

 smooth and not folded in any way. Many of these epithelial 

 cells bear short cilia on the free surface, but among these are 

 numerous cells (G.), which are, like goblet-cells, swollen or 

 flask-shaped, due to the presence of some secretion to which 

 they give rise. These cells generally appear to be empty, 

 having discharged their secretion, which in some cases can be 

 seen issuing from the cell into the cavity of the stomodseum 

 (PI. 26, fig. 18). These secreting cells occur chiefly in the 



