536 W. H. LONGLEY 



day and night, free and confined, wholly beyond the control 

 of the observer, or deliberately led from place to place upon the 

 reefs. So many of the Teleosts that are common at the Tortugas 

 during the summer have been studied, that it is believed that 

 false conclusions flowing from the study of unrepresentative ma- 

 terial have been avoided. The minimum amount of apparatus 

 has been used with full appreciation of the fact, that under such 

 circumstances charges of manipulation may not be urged with 

 any such show of reason, as that with which they have been 

 directed against Thayer's clever devices. 



The research has been in progress for about five years, yet no 

 one realizes more clearly than the writer that the intensive study 

 of one class of animals in a single region, though the species 

 studied be considerably more than a hundred, and the stations 

 at which observations were made, more than a thousand miles 

 apart, is little more than a reconnoissance in the field of so large 

 a problem. Still it seems that two conclusions may be safely 

 accepted: There is method in Nature's madness, and that method 

 is perfectly demonstrable by approved and conservative modes of 

 analysis. 



The results achieved speak for themselves. They might have 

 been obtained with great difficulty, if at all, with other support 

 than that of The Carnegie Institution of Washington, yet owe 

 such merit as they possess, far less to material assistance gener- 

 ously placed at my disposal, than to the unfailing interest and 

 support of Dr. Alfred G. Mayer, Director of the Department of 

 Marine Biology, to whom I remain permanently indebted. 



DETAILED STATEMENT OF RESULTS 



Counter shading 



Countershading is the definite gradation of pigment from 

 darkest on the mid-dorsal, or upper, to lightest on the mid- 

 ventral, or lower line. Its effect in destroying the solid appear- 

 ance of an object when it is exposed to uniform lighting from the 

 direction of its darkest surface is clearly demonstrated by 

 Thayer's countershaded models. Nevertheless, F. C. Selous 



