BREEDING BEHAVIOR OF SUCKERS AND MINNOWS. 21 



accompanied by ten or twelve small shiners (Notropis) and by 

 an occasional Campostoma. These formed a little school at 

 his sides and below him, and seemed to be waiting for fragments 

 from his feeding. 



2. Sexual Differences. In color the sexes appear to be alike 

 at all times. The back and sides are olivaceous, darker above, 

 with, dark irregular cross blotches. The belly is satiny white; 

 the lower fins are dull red. Thus the colors of the fish blend 

 with those of the stony bottom on which it is commonly seen. 

 I have determined the following percentage differences in fin 

 lengths (percentage D - = (M - F) : F) for males and females of 

 the same size based on a single female and the average of two 

 males: caudal - 4.5, anal 17.4, dorsal - 0.2, pelvic 4.2, pec- 

 toral - 2.5. These differences are probably within the limits 

 of individual variation except in the case of the anal. The anal 

 of the male thus shows the greatest excess in length over the 

 corresponding fin of the female. The upper and lower caudal 

 lobes are of about equal length in both males and females. 



This is one of the few species in which pearl organs are de- 

 veloped in both sexes. In the male (Fig. 7, lower male) they 

 occur on both surfaces of all the fins, on the upper surface of 

 the head, on the opercle and on every scale of the body and tail 

 except those of the ventral surface. The largest organs are 

 those on the anal fin, on the ventral half of the caudal and 

 on the sides of the tail, especially near the caudal fin. Those 

 of the anal reach a diameter of 0.8 mm. and a length of 0.28 mm. 

 in a fish 12 cm. in length, while on the caudal of the same speci- 

 men the organs are about 0.5 mm. wide, high and sharp pointed. 

 On the remainder of the fish the organs are small, 0.08 mm. to 

 0.25 mm. in diameter. All these organs make the surface rough 

 to the touch and are effective in proportion to their size. It is 

 again noteworthy that in the male the anal bears the largest 

 pearls for it is of all the fins the one that shows the greatest 

 percentage of excess length over- that of the female. In the 

 female the organs are smaller than those of the male but have a 

 similar distribution. They are absent from the dorsal fin and sides 

 of the body and from the ventral surfaces of pectoral and pelvic. 

 On the anal they are nearly as large as in the male, while on the 



