242 ECHIXODERMATA (tHE STARFISH) 



5. The Oral Surface. 



(1) Shape of the oral surface as compared with the aboral 



surface? Why this difference? 



(2) Spines. 



(a) Shape? 



(b) Position? 



(c) Arrangement? 



(d) Use? 



(3) Ambulacra, or tube feet. In the groove of each arm 



or ray observe soft disk-shaped structures. 



(a) Shape? 



(b) Size? 



(c) Number of rows? 



(d) Number in each row? 



(e) Total estimate for the entire animal? 



(f) How are these tube feet used? These tube feet will 

 be further studied in the internal dissection. 



6. The Nervous System. Find a whitish or yellowish cord 

 in the ambulacra! groove of each ray. 



(1) Trace it to its termination distally. 



(2) Trace it to its termination proximally. With what 



does it here unite? 



(3) Senses. Find the ' 'eye-spot" at the distal end of each 



ray. 



(a) Color? 



(b) Use? 



(4) Sketch plan of nervous system. 



7. Skeleton. 



Examine a dried specimen or, lacking that, dry a portion of 

 a ray for two or three days, then find the calcareous plates and 

 sketch the plan of structure for the skeleton. 



B. Internal Morphology 

 Cut along both edges of each ray. Lay each flap back, or re- 

 move it, taking care not to injure the delicate organs or the 

 madreporic plate. Dissect under water. 

 1. The Digestive System. 



(1) The Mouth. On the oral or under side, find the mouth, 

 (a) Size? 



