REPRODUCTION AND GROWTH 251 



people assemble to pick up these fish by moonlight, bonfire, 

 and flashlight, using various methods : hand, wire screens, 

 seines, etc. During the run thousands of fish may be 

 visible at one time ; their purpose is spawning. Male 

 and female burrow together at the wave margin and pair. 

 The eggs are laid in small masses or " pods " 3I inches 

 below the surface at a point far above the limit of an average 

 tide. They are even preyed upon by an Histerid beetle ! 

 The ova, which are protected by capsules, are very resistant 

 to desiccation. Ten days after the commencement of 

 spawning and one day before the first of the next high tides, 

 the eggs are washed out of the sand, hatch immediately, 

 and the larvae are free to escape into the surf. Though 

 errors of adaptation may occur, the whole procedure is 

 evidently wonderfully synchronised and adjusted so as to 

 allow the fish to lay their eggs on what is little less than 

 *' terra firma." The " runs " of fish begin at about the turn 

 of the tide and continue for about an hour ; the eggs are thus 

 laid as the water-line has reached its highest limit and in a 

 region which is out of reach of the succeeding tides. Eggs 

 laid an hour too early would get washed out again. Tides 

 accompanying the dark of the moon are always very much 

 higher than those of the full moon, and therefore uncover 

 all the eggs laid at the previous spring tide. If spawning 

 took place at the new moon, the eggs would have to wait 

 a month before hatching out, with correspondingly greater 

 risks from enemies and desiccation, etc. Eggs, however, 

 though on the point of hatching, are capable of lying quiescent 

 without harm for an additional fortnight if circumstances 

 make it necessary (Thompson and Thompson, 19 19). 



As a final illustration of periodicity on the sea-shore we 

 have the remarkable facts elucidated by Lloyd- Williams 

 (1905) with regard to the alga Dictyota. In this seaweed 

 the successive crops of sex cells are initiated, matured and 

 discharged within the space of a fortnight, and the course 

 of their development is governed by the time and height 

 of the tides. Consequently, a knowledge of the tides at 

 any given spot will enable one to predict almost the precise 



