STRUCTURE OF THE STARFISH. 



81 



similar in structure to the thickening in the ambulacra! 

 furrow. 



^-.. d 



PiQ.35. 



Fig. 35. — Diagram of a vertical longitudinal section through the 

 mouth pentagon in the axis of a ray, magnified about one himdred and 

 fifty diameters. (Copied with shght changes from H. Ludwig; Zeit. f. 

 Wiss. Zool. XXX. Taf. YL, Fig. 16.) 



a m. The first ambulacral plate, a'm'. The second ambulacral plate, 

 c w. Circum-oral water-tube. r ic. Radiating water-tube. m and m'. 

 Muscles which join the pair of plates, a m. m''. Muscles which join the 

 pair of plates a m'. a. Inner channel of circtun-oral peri-haemal vesseL 

 c. Outer channel of same, at the origin of the radiating iperi-haemal ves- 

 sel, d. Radiating blood-vessel, k. The partition which supports it 

 along the middle line )f the ray. e. Partitions which support the lateral 

 blood-vessels. 6,/, (7, ^, and p. As in Fig. 34, 



I 



