STARFISH 105 



On the bases of the spines find 

 15. The pedicellariae. — What is their exact posi- 

 tion with regard to the spines ? "What is their 

 shape? Size? Are they branched? Put one 

 under the low power and examine the struct- 

 ure. 

 Draw. 



The Skeleton. — In a well-cleaned specimen prepared as 

 directed notice 



a. General Structure. — Of what does the skeleton con- 

 sist ? How are the parts or ossicles arranged ? 

 Do you find any differences in the arrangement 

 of the parts on the oral and aboral surfaces ? To 

 what are the spines attached ? 

 "With a sharp knife cut off one of the rays at its 

 widest part, and examine its oral surface. 

 Forming the roof of the groove find 



I. The ambulacral ossicles. — How are they arranged ? 

 "What is their shape ? In what direction do they 

 run ? Do they bear spines ? Note the openings 

 or ambulacral pores, through which the ambu- 

 lacral feet pass. Are these openings perforations 

 in the ossicles ? If not, how are they formed ? 

 Are any two adjacent ambulacral ossicles exactly 

 alike in structure? 



Lying immediately outside the above is a sin- 

 gle row of 



c. The inter -ambulacral ossicles.— What is their 



shape ? Do they bear spines ? If so, are these 



spines similar to those on the aboral surface of 



the ray ? , 



Next outside the inter-ambulacral ossicles come 



