16 



on nearly all of the shells on the reefs in the upper part of the 

 1-ass shows that the embryos must have been abundant in the 

 water oyer these reefs at that time in their development when 

 they were ready to become attached. 



The distance of four miles, given as the least that any of 

 the spat on the reef nearest the head of the pass must have 

 traveled, is probably less than the actual distance from which 

 incst of them must have come, since by far the greater number of 

 'oreeding oysters were on the reefs about two miles below Lees- 

 burg, and thus one and one-half miles farther away. 



The currents prevailing in the pass are usually much 

 stronger during ebb than during flood tide, the difference being 

 most noticeable in the shallow water over the reefs in the uppei- 

 fart of the pass, where, under normal conditions, the current is 

 lunning down most of the time. No determinations of the com- 

 parative lengths of the periods of flood and ebb tides were 

 made during the time when the spat were settling on the reefs 

 in the upper part of the pass; but it is probable that the com- 

 parative duration and strength of the tides were not difl'erent 

 than at other times. 



As the result of these conditions it naturally follows that 

 only those embryos that began their free-swimming period near 

 the beginning of flood tide were at all likely to be carried to the 

 upper part of the pass, while those becoming actively motile 

 after flood or early ebb tide would find their place of attach- 

 ment in the lower part of the pass, or else be carried out into 

 the waters of the gulf. 



Although positive assurance of securing a set of spat in any 

 particular locality can be given only after experimental proof, 

 an assurance well within the bounds of probability can be given 

 when one has studied the currents in that region, provided there 

 are present adult oysters to furnish the spat. 



The size of the area over which a set of spat was secured in 

 Calcasieu •Pass during the past fall shows, when the compara- 

 tively small number of breeding oysters is taken into account, 

 that a few adult oysters have great power for restocking a de- 

 pleted bed or for providing a set of spat on any clutch exposed 

 in their vicinity. 



