202 ZOOLOGY. 



4. Ambulacral system. 



In a specimen from which the preceding organs have been removed, 

 make a transverse section of an arm about an inch from the disc. Find 

 the radial water canal, a small tube lying just outside the skeleton in 

 the ambulacral groove. Force air into it with a blow-pipe, or inject a 

 colored solution with a hypodermic syringe. What other structures are 

 affected? Trace connection between radial canal, ampulla, and ambulacral 

 feet. Compare the number of ampullae and the number of feet. Follow 

 the radial canal toward the disc. How does it terminate? 



From the madreporic body trace the S-shaped stone canal toward the 

 oral surface. How does it terminate? 



Ring canal: its position. Are there any other structures (sacs) in 

 communication with the circum-oral ring-canal beside the stone canal and 

 the radial water-tubes? form and position? 



5. Nervous system. 



There is a radial nerve (in the skin) superficial to the radial water 

 canal in each arm. The radial nerves unite to form a circumoral nerve 

 ring. 



6. Skeletal parts. 



Dried material and portions soaked for a day or so in a 10 per cent, 

 solution of potash should be used to supplement the alcoholic specimens. 



Is the skeleton complete, i. e., are the ossicles in contact? 



Are they similarly arranged on the aboral and oral surfaces? Which 

 surface shows the greater differentiation? Illustrate, and find a reason 

 if you can. How are the ossicles related to the spines? to the papulae? 

 Study with some care the ossicles forming the ambulacral groove, begin- 

 ning at the middle line. 



Ambulacral rafters : shape and arrangement. 



Ambulacral pores; are they in, or between, the ossicles? 



Adambulacral ossicles (just lateral to the former) ; how do these 

 compare in number with the ambulacral ossicles ? 



" Cross-shaped " ossicles. 



Which of the above bear spines? what kind? 



Place some of the cleaned ossicles in dilute hydrochloric acid. Result? 

 What is the significance of this result? 



7. Physiological experiments are possible only near the seashore. The 

 animals must be kept in sea water, and studied soon after being collected. 

 When possible, locomotion, the action of the ambulacral feet, feeding, and 

 sensitiveness should be studied. Do you find any indications, among the 

 specimens provided, of the power to renew a lost arm? With care and 

 perseverance, at the proper time of year, the sexual elements may be col- 

 lected and the maturation, fertilization, and cleavage of the ovum illus- 

 trated in this group. Teachers in inland schools should procure, when- 

 ever possible, slides demonstrating the early development of the star-fish 

 or sea-urchin. 



8. Compare briefly the external features of other " stars " with that 

 already studied. 



