1048 FRESH-WATER BIOLOGY 



like blade. This is not an intromittent organ but is apparently 

 used as a momentary clasper as the male darts at the female with 

 the lance directed forward and upward, liberating the spermatozoa 

 in spermatophores as the tip of the lance comes in contact with 

 the female. A single impregnation may furnish the female with 

 spermatozoa for several broods of young. 



The male of Amia has a caudal ocellus. In Rivulus it is the 

 female that possesses the caudal ocellus. 



The differences in disposition in the black bass, in which no 

 other secondary sexual differences exist, are mentioned elsewhere. 



FlG. 1544. Blunt-Nosed Minnow, Pimephales notatus (Rafinesque), $ . Actual size, 73 mm. long. 



The greatest display of secondary sexual colors is seen in the sun- 

 fishes and especially in the little darters and in Chrosomus whose 

 brilliant coloration is scarcely surpassed by that of the humming 

 birds. The greatest display of secondary sexual color takes place 

 just before the breeding season. It may be used as a sex recog- 

 nition mark, a battle flag, as in the rainbow darter, or as a lure to 

 the female. 



In many males small excrescences appear on the sides, on the 

 fins, or on the head during the breeding season. The anal fin is 

 often provided with booklets in suckers. The male of Campostoma 

 becomes covered with tubercles. Pimephales develops short, warty 

 horns on the head and the horned dace (Semotilus atromaculatus) 

 large, long ones. Some of these are used as excitants for the fe- 

 male, others undoubtedly to enable the male to cling to the female 

 during the spawning act. 



Physical Environment and Adaptations to it. With the excep- 

 tions noted, fishes are always found in water. The character of 

 the water, i.e., the per cent of salt and other chemicals in solution, 

 determines the three major ecological divisions of fishes: I, the 

 marine fishes; II, the brackish water fishes; and III, the inland, 



