ON THE DIPLOOHOBDA. 411 



of the epistome^ and remarks that Allman's figure " conveys 

 quite a wrong idea of the organ." The same remark 

 would be equally applicable to his own. He described 

 the epistome as extending "right across the oral side of 

 the animal from right to left/^ and figures it in the same 

 way (fig. 7). As a matter of fact it is continued as a con- 

 spicuous ridge on either side to the very tip of the spiral, 

 continuous throughout the three coils of the lophophore. If 

 the tentacles be regarded as forming the incomplete lateral 

 walls of a spirally coiled chamber, then the epistome forms 

 the floor of this chamber except for a fissure between it and 

 the outer row of tentacles through which the mucus strands 

 pass down into the oesophagus (fig. 58). This floor descending 

 from the apex to the base of the spiral must necessarily serve 

 to prevent access of the greater portion of the water-current 

 into the oesophagus, and to cause it to flow out in the median 

 line through the gap in the inner row of tentacles where it 

 would join the current along the hydrophoral area of the 

 outer surface of the tentacles. 



The figures 60, 61, and 62 should make tliis clear. In fig. 

 60 the lophophore is viewed from above, and the epistome 

 (shaded) is seen projecting over the mouth. The currents 

 are shown by the arrows descending the coils and passing 

 through the tentacular gap to escape over the anal area. 



Fig. 61 is a section through fig. 60 at a, showing the course 

 of the water first separated by the intertentacular filtration, 

 and further down the course of the water impinging upon the 

 upper surface of the epistome. In fig. 62, a section through 

 B, this water is seen to pass out through the tentacular gap, 

 whilst the mucus strands continue their course down the 

 oesophagus. The epithelium of the trophophoral area is 

 indicated by thick lines, that of the hydrophoral by thin. 



Conclusion. 

 My labours upon the Diplochorda (Phoronis and 

 Cephalodiscus) have now extended over some time. We 

 may here refer to some of the results. 



