80 COMMISSION OF CONSERVATION 



The length of the period during which spawned eggs remain quiescent 

 or are moved only by forces outside themselves is about five hours. 



Spawning may be turned to advantage by man, either in furnishing 

 him with eggs for artificial propagation or in giving the time from which 

 to make calculations for other processes, such as putting out of cultch. 



Swarming (swimming) is the name I give to the second important 

 event in the life of the oj^ster, affording practical information to man. It 

 represents the free-swimming period — the period of the larva — and 

 begins about five hours after the eggs are spawned. 



The manner of observing the swarming does not depend upon handling 

 adult oysters as spawning does. Neither does it depend upon watching 

 the swarmers or larvse in their natural habitat in the sea; that would be 

 as difficult as the actual observation of natural spawning. It depends 

 upon a method of straining sea-water and in this way collecting the swarm- 

 ing microscopic larvae. A plankton* net is towed behind a boat through 

 the water above oyster beds and the collected larvse are kept in glass 

 vessels full of sea-water and examined with a microscope. 



This is the most recent and most productive of practical methods. 

 It can be conveniently and repeatedly employed . It allows great quanti- 

 ties of water to strain through the net and retains great numbers of larvae. 

 It collects many ages and sizes extending over the longest and most form- 

 ative period. It exhibits actual conditions. It can be applied at the 

 right time. 



The method first passed beyond its incipient curiosity stage in 1904 

 when I made it the basis of my plans for following up that portion of the 

 life of the oyster which had remained unknown and brought it into system- 

 atic daily use as a necessary part of my programme. The value of the 

 method was proved by the results. 



An examination of Nelson's reports shows that he had used filter 

 paper in 1903, but did not make much use of it until 1906, when he wrote: 

 "In order to ascertain whether or not oyster fry are present in the water 

 it is necessary to filter it through a fine filter, which is a slow process." It 

 takes an hour or longer to filter a pailful of water. The larvse cling to the 

 paper or are washed under its folds so that it has to be opened out and 

 rinsed. The sediment has to be examined with a microscope. Nelson 

 employed this method a great deal in his later work. It gives the pro- 

 portion in number of larva? to the volume of w^ater filtered. But when 

 larvae are scarce such small quantities of water might not yield any and 

 thus lead to wrong results, especialty if used to determine the time of the 

 first occurrence of larvjE in an oyster region. Some of the larvse may be 

 easily overlooked, and in small catches this would greatly modify the pro- 

 portion. In 1907 the temperature on June 18 was 70° F. and the first 

 undoubted larvse were obtained on the 25th or 26th. On July 5th, a half 

 * See footnote to page 31. 



