THE PHILOSOPHY OF XESURUS 293 



ideal scraping organs, and my comparison with a 

 hoe had better be replaced with that of a rake. 



The nostrils were far out of the way near the 

 eyes, for they can be of slight use, there being little 

 or no selection of the scraped-off nourishment, and 

 if placed nearer, they would only become clogged 

 with debris in suspension. The eyes were of good 

 size and very protuberant, standing well out above 

 the surrounding, rather concave head area. Their 

 rotating power was unusually great. With a 

 normal divergence of 8° forward, and 12° down, 

 which alone focussed them well toward the ap- 

 proaching rocks, they could be rotated forward and 

 downward through an angle of 42°. Not only was 

 the elevation and direction of the eye thus a special- 

 ization for the direct observation of the feeding 

 grounds, but the cheeks were hollow, and the 

 elongated bridge of the face deeply concave, thus 

 affording an unobstructed field of vision. This 

 was another powerful argument for the absence 

 or relative lack of enemies, that all this complicated 

 architecture was for clear vision ahead, not behind, 

 — Xesurus was in no sense a pursued one. 



The pattern and coloration were not protective, 

 and if they were, the enormous schools would 

 render any concealing coloration of no avail. The 

 pale blue grey, with the two broad, black bands, 

 the large, silvery iris and whitish lips, and above 

 all the brilliant yellow tail, and yellow and black- 

 banded line of the caudal plates, rendered it an 

 object easy of detection among the variously 

 colored rocks on which it fed. I should rather 



