250 EXPERIMENTS AND OBSERVATIONS 
land it is more abundant than at any other part of the British coasts, 
several specimens having been taken in Loch Fyne and the Firth 
of Clyde. It has been taken on the coast of Denmark, but not on 
that of Norway. 
Peculiar habits, differing from those of other flat fishes, have been 
observed in living specimens of two species of Zeugopterus, namely, 
punctatus and unimaculatus. ‘The fish are seen in aquaria to be 
nearly always adhering to the vertical sides, remaining in one place 
for a long time, and keeping themselves suspended in this way in a 
vertical position without any difficulty. Other flat fishes occasionally 
assume this position, but are unable to retain it for more than a few 
seconds or minutes. This habit was studied by the late Mr. George 
Brook, F.Z.S., who described his observations in two papers.* In the 
first of these he refers only to Zeugopterus unimaculatus, of which he 
took several specimens in Loch Fyne in a small sandy bay. They 
usually adhered to the sides of the tank in which they were placed, 
although found on this sandy ground overgrown with Zostera or sea- 
grass. The body was slightly raised from the glass with the lower 
surface of the unpaired fins tightly pressed against it. A current of 
water is stated to have passed from the branchial chamber of the 
lower side along the space between the body and the glass and out 
behind, this current being caused by a rapid vibratory movement of 
the accessory portions of the dorsal and anal fins. ‘The accessory 
portions of the fins appeared, therefore, ‘to be specially constructed 
to aid in the respiratory function.” In his later paper Brook states 
that he was inclined to think he laid too much stress on the action of 
the accessory flap. ‘‘ The basal portions of the vertical fins are kept 
in constant motion, but this motion is more vigorous in the rays 
immediately in front of the tail than in the accessory flaps situated 
underneath it.’ Brook did not attempt to explain the method by 
which the fish was enabled to adhere to the glass or other vertical 
surface and maintain itself in a vertical position. 
My own observations in the Plymouth Laboratory have been made 
on Z. punctatus, and my object was to ascertain what force kept the fish 
ina vertical position against a vertical surface, and how the force was 
produced. ‘I'he fish lives well in confinement, and is not timid or violent 
in its movements when disturbed. It is not difficult, therefore, to guide 
it to the glass front of the tank and persuade it to adhere there, so that 
observations and experiments can be made with it. It was evident 
that the adhesion of the fish was not produced by ordinary sucker 
action—in other words, by hydrostatic pressure, because the space be- 
neath the body was freely open to the outside water in front dorsally 
* Tehthyological Notes, Fourth Ann, Rep. Scot, Fishery Board ; Notes on the British 
Species of Zeugopterus, Proc. Roy. Phys. Soc. Edinb., Session 1886-7. 
