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HANDBOOK OF INVERTEBRATE ZOOLOGY. 



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

 oral nerve of Lange. 



Fig. 34. 



Fro. 34. — Vertical section through the mouth-pentagon in the plane 

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

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

 Taf. VI., Fig. n.) 



i a. Inter-ambulacral ossicle, m. Muscle which runs between ambu- 

 lacral plates of adjacent rays, c w. Circum-oral water-tube. h. Epithe- 

 lium of perivisceral cavity. /;. Perivisceral cavity. ;>. Peristome. 

 a. Inner, and c. outer division of circum-oral peri-htcmal vessel. 

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

 division of the peri-haimal 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 (j9). Observe that it is 



