As a general rule, the fish in this book are shown swimming from right to left across the page. But it would be a solecism to show soles so doing. The reason is that flatfish, which belong to the Order Pleuronectiformes, have both eyes on the same side of the head; some (the sinistral flatfish) on the left side and some (the dextral flatfish) on the right. Dextral flatfish, for example soles, must therefore be portrayed swimming from left to right.
The reason for this strange arrangement of the eyes is that the flatfish are adapted to lurking on the sea bed on their sides and need to have both their eyes on top. They like to half-bury themselves in the sand and have a coloration which renders them almost invisible when they do so. They can ‘disappear’ in this way with remarkable speed. Buckland describes an incident on the coast of Kent when a seine net full of plaice rolled over, and the plaice started to escape.