JOURNAL OF MICROSCOPICAL SCIENCE. 
EXPLANATION OF PLATE IV, 
Illustrating Mr. Stewart’s paper on the Minute Structure 
of certain Hard Parts of the Genus Cidaris. 
Fig. 
1.—Sector of a transverse section of the primary spine of Cidaris annulata. 
2.—Upper part of a pedicellaria of the same, including the head and portion 
of the stem; the faint shaded bands seen through the transparent 
lower part of the head indicate the closing muscles of the jaws. 
3 and 4.— Varieties presented by the jaws of this species. 
5.—Transverse section of the lower part of the head of a pedicellaria, 
showing the chambers of the jaws and the three bands of muscles 
which close them. 
6.—Spicula of the ambulacral tubes. 
7.—Spicula of the ovary. 
