FISH signals of 45S rDNA (red) (A, C), silver staining (B, D) in S. rufescens (A, B) and S. fluminensis (C, D). Arrows in A and C indicate distended secondary constrictions, and arrowheads show condensed rDNA sites. Arrows in B and D indicate larger silver signals and arrowheads in B shows small sites. Scale bar: 10 µm.