STRUCTURE OF SPINES 67 



smaller elevations, the miliary granules. In 

 addition to the spines, the pedicillariae are 

 also supported on the top of these tubercles. 

 The spines, like the tubercles, are of three 

 sizes, primary, secondary, and tertiary, and 

 the structure of each is fundamentally the 

 same. Each spine consists of a long shaft 

 marked by longitudinal flutings ; the base is 

 hollowed into a cup or condyle, which fits 

 over the pimple of the tubercle. Each spine 

 is furnished with a collar which serves for 

 the attachment of the muscles which fix it 

 to the test. 1 (A Treatise on Zoology.) 



The transverse section, as in the illustra- 

 tion, shows that the spine is made up of a 

 number of solid wedges radiating from a 

 central axis, and separated by bands of porous 

 tissue. 



The sections vary in design in the spines 

 of different kinds of sea-urchins. Thin 

 sections of spines make very beautiful objects 

 for the microscope. Patterns for rose 

 windows, for lace, and other forms of orna- 

 mental handiwork may be obtained from these 



