14 INTRODUCTION TO SEXUAL PHYSIOLOGY 



and each time upon or near the day of the last quarter of the moon 

 and with the first rays of the sun, and allied genera also show a 

 regular periodicity in breeding. 



Many other instances might be given of the adjustment of 

 breeding habits to environmental conditions and the stimuli 

 which these give to sexual activity, but we will content ourselves 

 with one more example cited by Flattely and Walton. The 

 " grunion " (Leuresthenes tenuis), a small smelt inhabiting the 

 sandy shores of California, breeds in the spring from March to 

 June. On moonlight nights during the big tides on the second, 

 third, and fourth nights after full moon, very shortly after high 

 tide, this fish " comes in with the sweep in the water, and, as the 

 waves break, lies for a moment, squirms, and drops back into the 

 wash of the next wave." At the wave margin the male and female 

 burrow together and pair, the eggs being deposited below the 

 surface at a point considerably above the limit of an average tide. 

 Before the next big tide the eggs are washed out of the sand and 

 hatch immediately, the larva3 escaping into the surf. Thus the 

 procedure is so adjusted as to enable the fish to lay their eggs 

 at the highest limit of the water line and out of reach of the 

 succeeding tides. 



The periodicity which is so constant a feature of sexual hfe 

 among mammals is dealt with in a later chapter. 



