80 . HANDBOOK OF INVERTEBRATE ZOOLOGY. 



floor of the outer peri-hsemal channel. This is the circuui- 

 oral nerve of Lauge. 



la 



FIG. 34. 



Fio. 34. Vertical section through the mouth-pentagon in the plane 

 of an inter-radius, magnified about one hundred and fifty diameters. 

 (Copied with slight changes from H. Ludwig; Zeit. f. Wiss. Zool. xxx. 

 Taf. VI.. Fig. 17.) 



i a. Iriter-ainbulacral ossicle, m. Muscle which runs between ambu- 

 lacra! plates of adjacent rays, c tc. Circum-oral water-tube. //. Epithe- 

 lium of perivisceral cavity. b. Perivisceral cavity. p. Peristome. 

 a. Inner, and c. outer division of circum-oral peri-ha'inal vessel. 

 I. Thickened pad formed by the epithelium of the floor of the outer 

 division of the peri-hannal vessel. /. Fibrous layer of surface epithe- 

 lium, g. Granular layer of the same. 



9. The thickened ridge of surface epithelium (g) which 

 forms a ring around the mouth between the water- 

 tube (civ) and the peristome (p). Observe that it is 



