210 



ZOOLOGY. 



FIG. 98. Diagram of a portion of the water-vascular (ambulacral) system of the 

 Starfish, a, ampullae; f, ambulacral feet; m, madreporic body; p, Polian vesicles; r.c., 

 ring canal, with the upper portion removed at the right of the figure; r.t., radial 

 water lubes (in r.t/ the upper portion is removed at the distal end and the proximal 

 portion is represented entire) ; s, stone canal. 



Questions on the figure. Where does the water enter this system 

 of vessels? At what points in the system is it of use? By comparing all 

 illustrations at your disposal, describe the mode of using this system of 

 organs for locomotion. How may it be used in respiration? 



body is capable of definite and considerable contractions, by 

 reason of both circular and longitudinal fibres. In forms 

 with incomplete skeletons, as the star-fish, muscular fibres 

 connect the ossicles and there is a degree of flexion of the 

 arms. There are also special muscles controlling the water 

 vascular system, the stomach, the mouth parts, the spines and 

 pedicellarise. The fibres are non-striate. 



246. The Nervous System consists of a ring around the 

 mouth and a radial nervous band in each arm supplying, by a 



