200 MORPHOLOGY OF IXYKRTKBRATE TYPES 



showing the stem with the calcareous axis and the head with 

 three jaws. 



6. Find on the test a similar pedicellaria with jaws open and 

 make a drawing of it. 



7. Find on the test the second type of pedicellaria in which 

 the axis does not reach to the head. Make a drawing of it 

 under microscope. 



8. Remove an ambulacral tube (tentacle), from the aboral 

 surface of the test, examine it in the same manner and make a 

 drawing of it. 



9. Find the five terminal tentacles on the oculaf plates. 



10. Carefully clean the entire aboral surface of the test with 

 a toothbrush or examine a dried and cleaned test. Make a 

 large drawing showing the periproct with the four anal plates, 

 five genital plates with the genital openings, five ocular plates 

 with pores for the terminal tentacles, five radii and five inter- 

 radii with the zigzag suture between the tw r o rows of plates, the 

 tubercles on the interradial or adambulacral plates and the 

 tubercles and pairs of ambulacral pores on the radii. Once more 

 examine carefully the genital plates and find among them the 

 one which serves also as madreporic plate. Show with a dotted 

 line the plane of bilateral symmetry. 



11. Make a drawing of the oral surface of a dry specimen in 

 which the spines and the peristomial membrane were removed. 

 Show the arrangement of the spine tubercles, the peristomial 

 edge of the test, the ambulacral pores and the first and second 

 adambulacral plates folded back upon the two following plates. 



12. Holding the test in your hand so as to look into the body 

 cavity under an angle to the dorso-ventral axis, examine with 

 naked eye the peristomial edge of a radius and make a drawing 

 twice the natural size showing the auricles. 



13. Returning to the cleaned alcoholic specimen make an 

 incision around the equator. Strong scissors may be used for 

 this purpose, but a very fine saw is preferable. Carefully open 

 the specimen by cutting the mesenteries of the alimentary canal, 



