536 



Marvels of the Universe 



Photo 60] 



SEA-FIR. 



[ir. \\\il. L.D.S. 



A portion of a branch of tfie species known as tfie Sea-Oak Coralline. 

 The ordinary polyp-cells are here arranged in pairs. The large capsule is 

 that in which the young are produced. I Enlarged about twenty times.' 



to seek the sandy bottom of the 

 sea. Here it lay half-hidden in 

 the silt until the upper surface 

 became brown and the left side de- 

 veloped into the under side, which re- 

 tained (except in rare instances) its 

 original white colour, while the fins on 

 the back and belly took their place 

 along the sides and the under eye 

 moved to the upper side. 



Flat-fishes are not really of different 

 construction from other fish, as will be 

 seen by the following homely illus- 

 tration. Let the reader picture a fish 

 — sa}-, for e.Kample, a salmon — at rest 

 in the ordinary position of swimming. 

 Consider now pressure being applied to 

 its two sides so as to squeeze them 

 more and more together, until at last 



the fish becomes quite flat. The sides 

 remain sides just as before ; and we 

 have only to suppose the salmon turning over to swim on one of them like the plaice, and we 

 have the condition e.xplained. 



The most remarkable part of this transformation is the change in the position of the eye. The 



turning over of the eye was for a long time considered a problem and was thought to be due to a 



positive shift of one eye to the other side of the skull ; but anatomists now show the whole thing is 



due to a twist of the bones of the face which slowly and gradually takes place during the fortnight. 



It is now easy to realize the necessity which brought about the change. The fish is henceforth 



adapted to its mode of life. It is now 

 able to use the second eye, which in its 

 original position would have been use- 

 less. At the same time it can lie un- 

 noticed on the sand owing to the 

 similar coloration of its upper surface ; 

 and also it wiU be able, when dis- 

 turbed, to make use of its two large 

 fins to fhcker away with that quick 

 undulating movement which is charac- 

 teristic of Flat-fishes. This movement 

 is essentially due to the peculiar 

 character of the transposed fins, which 

 are attached to the body in the usual 

 manner of back fins, but not after the 

 fashion of side fins, for these can be 

 spread out from the body. It should 

 also be noticed that the breast fin of 

 OBELiA. the fish has since the period of trans- 



The polyps are here arranged alternately on each side of a slender stem S formation beCOme USeleSS OWlug tO itS 

 wKich runs over the leaves of Sea-grass, The polyps ultimately float off as 



Photo &y] 



IFlaiters X- Co., Loiigsight. 



linute free-swimming jelly-fish. (Slightly enlarged.) 



peculiar position on what is now the 



