“…It has been recommended that we must select the contrast agent(s) effectively to enhance the contrast (Gignac et al, ; Metscher, , ; Smith et al, ). Recently, studies of micro‐CT observations for the brain of various animal taxa have been published (e.g., mammals, de Crespigny et al, ; Saito & Murase, ; birds, Gignac & Kley, ; Masis et al, ; fish, Kotrschal et al, ; insects, Smith et al, ; Steinhoff et al, ; cephalopods, Kerbl et al, ; Liu et al, ). Also, the contrast agents that are suitable for micro‐CT observation have been determined in some animals (Metscher, , ; Pauwels et al, ).…”