SPAWNING HABITS OF CHROSOMUS. 1/ 



were small, while in the pools below were larger schools which 

 took no interest in spawning, and were comparatively inactive. 

 The males of these latter schools had nearly lost their bright 

 colors. Evidently the breeding season was nearly over. At this 

 time many of the eggs had hatched out. 



During this prolonged breeding season, extending over fully 

 a month, the stream was frequently swollen by freshets, which 

 presumably interfered with the spawning operations. 



Discussion. — As shown by the unison of their circling move- 

 ments when not engaged in spawning, and by the fact that they 

 occur in schools even after the spawning season is over, these 

 fishes possess a strong gregarious instinct. The two conspicuous 

 longitudinal dark stripes on the sides of the bodies of both sexes 

 probably serve as recognition marks. 



The distribution of pearl organs over practically the entire body 

 of the male affords a roughened surface which during spawning 

 aids him in keeping his position beside the female. The function 

 of the pearl organs of the Cyprinidae was first discovered and 

 described by Reighard ('03). The structure of pearl organs has 

 been figured by various writers. 



The greater size and strength of the pectoral fins of the male 

 as compared with the female, and the fact that the dorsal surfaces 

 of these fins are unusually well provided with pearl organs, indi- 

 cate that these fins are of use to the male in holding the female. 

 The male, coming up from the rear, doubtless interlocks his 

 pectoral fin between the pectoral fin and the body of the female, 

 though it was impossible to see this. 



The excessive number of males present on the spawning grounds 

 is perhaps correlated with the method of spawning, since two 

 males spawn with a single female. 



The observable factors in sex recognition are : the brilliant 

 colors and aggressive bearing of the male ; the dull colors, 

 swollen abdomen, and timid, hesitating movements of the female. 



It is significant, in its bearing on current theories of secondary 

 sexual characteristics, that the female showing the secondary 

 sexual characters of the male was an unusually large and apparently 

 vigorous specimen ; but it would be unwise to base conclusions 

 on a single instance. 



