BREEDING BEHAVIOR OF SUCKERS AND MINNOWS. 9 



female 2.6 mm. In smaller individuals there is no great differ- 

 ence between the length of fins in individuals of opposite sexes, 

 but these differences appear with increasing size. A male of 135 

 mm. when compared to a female of 137 mm., had slightly shorter 

 dorsal, caudal and pectorals, but somewhat longer anals and 

 pelvics. 



It is to be noted that in adult specimens those fins of the 

 male (lower caudal lobe, anal) that bear the largest pearl organs 

 also exceed the corresponding fins of the female by the largest 

 percentage. (Cf. Table I. and Fig. I.) Indeed the fins of the 

 male may be divided into three groups on the basis of the per- 

 centage by which they exceed the corresponding fins of the 

 female; the anal and caudal with 31 per cent, excess; the pec- 

 toral and pelvic with 10 to 20 per cent, and the dorsal with 

 5 per cent. The size of the pearls borne on the fins of these 

 three groups is roughly proportional to these percentages. 



When the fish are seen close at hand, or under favorable 

 conditions with field glasses, the pearl organs of the male and 

 the greater size of his anal fin suffice to distinguish him from the 

 female (Fig. i). But were the sexes identical in form, size and 

 color, the behavior differences described in another place would 

 differentiate them. 



5. Breeding Activities. During the. breeding season males are 

 at all times much more numerous on the rapids than females 

 and during the greater part of the time none but males are 

 present. It does not follow that males are actually more num- 

 erous than females. On the contrary data that I have collected 

 at other localities and at times when the fish were not breeding 

 indicate that the males and females are equally numerous. 

 (Reighard, 1915.) In the breeding season the females do not 

 mingle with the males on the rapids until ready to lay their eggs. 

 But from time to time a female comes from her retreat in the 

 deeper water above or below the rapid or from beneath the 

 bank and takes her place on the rapid. If no males happen to 

 be near she may lie quiet in one place for a considerable time. 

 But if males are near they at once approach her, sometimes one 

 or two, sometimes as many as ten. Pairing is best seen when 

 but two males are involved and will be first described under these 



