FISHES 



351 









Photograph by J . Arthur Button 

 FIG. 134. Cycloid scale of herring, showing transverse radii. 



A further examination of ctenoid or cycloid scales 

 shows various interesting features. The surface is 

 marked with numerous fine lines, which are usually con- 

 centric, but in some cases transverse or longitudinal. 

 These are the circuli; they are not growth rings, as 

 some have supposed. There are, however, more or less 

 distinct rings called annuli, due to irregularities of 



square gummed labels, each overlapping one side of the cover glass, or if a 

 second slide is used, the labels may bind together the ends of the slides; 

 write the data on the labels. After a day or two the scales will be dry, and 

 the clamps may be removed. The scales will remain in place without further 

 attention. 



