178 MICROSCOPY FOR BEGINNERS. 



directed forward. From each scale there arises a stout, 

 recurved, unequally and minutely furcate spine, whose 

 base is enlarged and thickened. These spines do not 

 commonly originate from the centre of the scales, but 

 near the posterior part, and between the margins of 

 those laterally contiguous. The spines are largest and 

 stoutest on the back proper, decreasing gradually over 

 the neck and head, and rapidly over the posterior parts, 

 while across the dorsal surface immediately in front of 

 the caudal bifurcation there extends a supplementary 

 series of four thorns, longer and stouter than those on 

 any other part of the body. The posterior region of 

 the space between the longitudinal ventral bands of 

 cilia bears five bristles, arranged to form a long triangle, 

 the apex pointing forward. 



The eggs vary considerably in external ornamenta- 

 tion, showing three patterns. In one, the ends and one 

 side bear low, stout, hollow processes, whose apices are 

 truncate, and four or five parted when viewed from 

 above. In another, the appendages are long, hollow, 

 conical spines, whose distal ends are trifid or quadrifid, 

 the branches in profile appearing very fine and delicate, 

 but when viewed from above are seen to taper to the 

 ends, where each terminates in a widely spreading fur- 

 cation. In the third form, one side and both ends are 

 covered by an irregular net -work of raised lines, the 

 meshes being four or five angled, while the opposite 

 side is rugose with fine, minutely sinuous lines. 



