ADJUSTMENT OF FLATFISHES 455 



can see is not necessarily the same as what it commonly does see. 

 It may well be that the animal's attention is chiefly centered upon 

 areas which do not rise much above a horizontal plane. I shall 

 discuss this point more fully later. 



Rapidity of these changes 



The average time required by Lophopsetta to attain the highest 

 degree of pallor, commencing with the dark state^^ was probably 

 less than two days, and the change was commonly noticeable within 

 a single day. One particularly refractory specimen was kept for 

 four days in a white box before any undoubted change occurred. 

 The change, when it did come, was rather abrupt, though the 

 highest degree of pallor was not attained until the lapse of 6 to 

 7 days. Specimens were found, on the other hand, which changed 

 decidedly within a few hours, when placed for the first time in a 

 white tank, and, in one case at least, the maximum degree of 

 pallor was assumed in less than twenty-four hours. 



After the first experience of this sort, it happened, in many 

 cases at least, that subsequent changes were undergone much 

 more rapidly. Thus specimens which required several days for 

 the first change to the pale shade often completed this change with- 

 in a few hours, after one or more such transpositions. One dark 

 fish, for example, when placed for the first time in an all-white 

 box, showed little or no evidence of paling after one day, and did 

 not blanch to the fullest extent until the lapse of about three days. 

 After being returned to black, it was recorded, at the end of 19 

 hours, as being nearly or quite as dark as originally. When trans- 

 ferred to the white box for a second time, the fish became decidedly 

 paler in less than a minute, and within an hour was nearly or 

 quite as pale as at any time previously. 



Whether or not a similar shortening of the reaction-time may be 

 brought about in the case of the reverse change, i.e., from fight 

 to dark, was not fully determined. A change in this direction is, in 



*9 Nearly all of the specimens, when first brought into the laboratory, were 

 much nearer the darkest than the lightest condition. They were, too, frequently 

 kept for some days before being used, in a large stock tank, painted black withia. 



