I I 26 



BUI,I,ETIN OF THE BUREAU OF FISHERIES. 



ning is as wide as the pit, but as it is followed downstream gradually narrows 

 to a point (5. T., in fig. 9, pi. cxviii, and fig. 3, text). 



As the observer approaches one of these structures he may see the flash of 

 a fish departing from the pit, and he is then apt to move on in the belief that 

 nothing more is to be seen. But if he lies prone on the bank and keeps per- 

 fectly still the fish will return. This may happen after ten or fifteen minutes, 

 or it may not happen for an hour, and during all this time the observer must 

 remain motionless, not moving so much as a hand or foot, for if he moves the 

 fish at once flees to shelter and does not reappear for some time. It again 

 departs if the movement is repeated, but each absence is shorter than the pre- 

 ceding, and after a time, if the movements are not too abrupt, the fish 

 remains on the nest in spite of them. For him the observer has become a part 



Tig. 3. — Showing in longitudinal section the nest of a horned dace with the male and female fish on the nest. The stream 

 flows in the direction indicated by the arrow at the upper left corner of the figure. 



of the landscape, to which he pays no more attention than to a tree. The fish 

 that returns (fig. 10, pi. cxviii) is usually 8 or 10 inches long, of a beautiful apple- 

 green color above and of a rose red below. If a small fish, there may be a 

 stripe of dark brown between the two colors, where they join along the middle 

 of his side. At the base of the dorsal fin in front is a black spot (fig. 12, 13, pi. cxix), 

 and above this an orange spot, while the caudal and paired fins are yellow. If 

 the observer is very near, or if he uses field glasses, he may see along the sides 

 of the head above the eye and nostril a row of 4 or 5 white horn-like spines (fig. 

 10, pi. cxviii, and text fig. 5, p. 1 130). These are pearl organs, so called because 

 in some related forms they have the rounded glistening look of pearls (see fig. 4, 

 pi. cxv, on the snout). By them and by its colors the observer may recognize 

 the fish as the male of the horned dace. 



