ADJUSTMENT OF FLATFISHES 417 



fragments of lava, tufa, shells and pottery, constituting the sea- 

 bottom in the vicinity of Naples.^^ 



In considering the appearance of this fish upon a given bottom, 

 it must be borne in mind that the marginal fins (homologous with 

 the dorsal and anal) are translucent, or indeed at times nearly trans- 

 parent, and that through them the underljdng bottom may 

 commonly be seen distinctly. In this way, the harmony of appear- 

 ance between fish and bottom is oftentimes greatly enhanced. 

 When resting upon a bottom of sand or fine gravel, the fish fre- 

 quently covers over the marginal fins, and sometimes more or less 

 of the remaining skin surface, with the material at hand. This it 

 does by a rapid undulatory movementof the body, by which it 

 stirs up the sand or gravel and settles down into it. 



Methods 



The specimens were kept in glass jars, either circular or rect- 

 angular in form, and commonly supplied with sea-water from a 

 large tank by means of siphons. When natural materials were 

 employed for the background, ^-^ these were emptied directly into the 

 bottom of the jar. Artificial backgrounds were produced by painting 

 the bottom of the j ar directly, or bj^ painting glass plates which could 

 be inserted at pleasure. An account of the different types of 

 background employed in these experiments will be deferred until 

 I come to a consideration of the results which were obtained. 



The fishes were kept for longer or shorter periods under the 

 various experimental conditions, notes and descriptions being 

 made from time to time. Since verbal descriptions of such phe- 

 nomena are necessarih^ quite inadequate, frequent photographs were 

 made. In order that the colors assumed might be recorded with 

 approximate accuracy, reference was in many cases made to the 



'^ I do not mean by this to imply that there is any specific adaptation to this 

 particular locality. Sands and gravels of a very similar appearance, though differ- 

 ing widely in their mineralogical composition, are doubtless to be found all over 

 the world. Samples of gravel which I brought back with me msfy be matched, as 

 regards their general appearance, by gravels collected in the vicinity of Woods Hole. 



" I have throughout used the word background to designate the surface upon 

 which the fish lay. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 10, NO. 4 



