PROPAGATION 61 



Guarding the Empty Nest. — When the nest has been pre- 

 pared the male remains on guard over it, but makes frequent 

 circles into deeper water as though in search of the female. 

 The time between the completion of the nest and the actual 

 spawning may be but a few minutes, as in one case that I 

 observed, or it may be some days. The length of the interval 

 depends, in part at least, upon the temperature. The males 

 may begin nest building in a temperature somewhat below 

 60 degrees F., but the females do not spawn until the water 

 has reached a temperature of between 62 degrees and 65 

 degrees F. If the male does not begin nest building until 

 the water has reached 62 degrees F., the spawning may follow 

 at once upon the nest building. If the male begins the nest 

 when the water is below 60 degrees F., spawning is delayed 

 until the weather conditions have brought the temperature 

 of the water to a suitable point. 



Spawning. — After the male has guarded the nest for a 

 time he returns from one of his excursions into deeper water, 

 accompanied by the female. At most seasons there appears 

 to be no external difference between the sexes, so that it is 

 impossible to distinguish them without dissection. At the 

 breeding time there is ordinarily no difficulty. The females 

 are then much thicker bodied and, particularly when seen 

 from behind and somewhat from above, may be distinguished 

 from the males by the form of the body, even at a distance 

 of from ten to twenty feet. Small females sometimes spawn 

 when they contain very few eggs and these of small size. 

 It is then not easy to distinguish the sexes by the form of 

 the body alone, and if there were no other method mistakes 

 might easily be made. But in all cases the behaviour of the 

 two sexes is so wholly different that the person who has once 

 observed it in a case where the sexes were easilv distinguish- 

 able by the form, need not afterward hesitate to distinguish 

 the sexes at the spawning time by their behaviour alone. In 

 addition to difference in form and behaviour, a marked differ- 



