THE STARFISH 



135 



if you have studied the living starfish. Since their functions are res- 

 piratory and excretory, the papulsB are sometimes called dermal gills. 

 Among the papulae and surrounding the spines are minute white specks, 

 some of which will be seen to be stalked; these are the pedicellariae 

 as noted if you have studied the living animal. With a scalpel scrape 

 off some of the pedicellaria), mount on a slide in glycerin, and examine 

 under the microscope; certain structural features of the pedicellariae 

 will be more clearly demonstrated if the tissue is macerated for a few 



Qbora/ neri/'e corc^ 



ep/cfermi3 

 -papu/a 



-pec//ce//ar/a 



cf/geet/Ve ^/ancf 



p/the//'am 

 gronaof 



ampuf/a 



raa//a/ cana/ 

 ■per/toneum 

 ^/(e/eta/ phte 

 mu5c/& etc, 

 foot 



^^uperf/c/a/ 

 nerye cord 



'cfeep 

 neri/e cord 



Fig. 63. — An arm of the starfish; diagrammatic cross section. 



moments in caustic potash before the mounting in glycerin. Material 

 from the dried specimen treated in this manner may also be used. 

 How many kinds of pedicellariae do you find? How many parts has 

 each? How do the jaws articulate? Where are the muscles attached? 

 Gentle pressure on the cover glass will sometimes cause the jaws to 

 open. Make a large outline of the starfish, to be completed as you 

 proceed with your dissection. Use the distal half of one arm of the 

 bivium for a drawing of the oral surface; and use the other arm of 

 the bivium for a similar drawing of the aboral surface. Label care- 

 fully. Reserve the region of the disk and of the trivium for the draw- 

 ing of internal parts. 



