102 NATURAL HISTORY OF AMIA CALVA LINNAEUS. 



2. Males may usually be distinguished from one another without taking them from 

 the water by accidental structural peculiarities, or more often by color peculiarities. 



3. About three times as many males as females come to the spawning ground. 



4. The nests are built on selected areas on the bottom, where there are usually 

 fibrous roots and little growing vegetation, and are often concealed. 



5. Nest-like areas of the bottom are often seen where the bottom is in dense 

 shade ; such areas may be used for spawning with little or no previous preparation. 



6. The nests are built by the male without assistance from the female by 

 rubbing, biting (?), and fanning away the vegetation and ooze so as to expose the 

 subjacent material. The nests are built mostly at night. 



7. Each nest is the property of an individual male. 



8. The nests may be very near one another or far apart. Their frequency 

 depends on the number of spawning fish and on the character and size of the 

 available spawning ground. 



9. Each male guards and defends the empty nest for a period of usually twenty- 

 four to thirty-six hours, but this period may be prolonged to six days, or possibly 

 longer. 



10. The males are found guarding the nests more often in the afternoon than 

 in the morning. 



11. If the females do not appear the males finally abandon the nests. 



12. The optimum temperature for nest-building and spawning is 16° to 19° C. 



13. The spawning is intermittent and occupies a period of from one to three hours. 



14. The spawning occurs usually at night; occasionally by day. 



15. There is no evidence that the bright colors of the male are in any way 

 sexually selected, and since spawning occurs chiefly at night, this would seem to be 

 impossible. 



16. Sexual excitation of the female is produced by the biting and rubbing of 

 the male. 



17. Two females may spawn at different times in the same nest with an indi- 

 vidual male. 



18. There is evidence that an individual female may spawn in the nests of two 

 or more males. 



19. The females are not seen on the spawning ground except when spawning. 



20. The nests when freshly filled with eggs and in open water are in this locality 

 frequently very conspicuous. 



21. The nests containing eggs are guarded by the male until the larvae are 

 about 12 millimetres long. 



