PRODUCTION AND COLLECTION OF SEED OYSTERS 231 
SPAWNING OF OYSTERS AND OCCURRENCE AND DISTRIBUTION OF OYSTER LARWE 
The time of spawning of oysters in Onset Harbor was ascertained by studying 
the plankton and noting the first appearance of the oyster larvse and by examining 
the gonads of the adult oysters. In the summer of 1927 plankton was collected with 
a small plankton net made of bolting silk No. 20, and weighted on its under side 
which bore a protecting strip of linen, so that the net could be dragged over the bot- 
tom or towed at any desired level. Five-minute tows were made every day at the 
surface, along the bottom, and at a level midway between. By towing at the same 
speed each time a fair estimate of the relative abundance of the larvse could be 
obtained. In 1928 quantitative plankton samples were taken by means of a rotary 
pump and a hose lowered to the desired level. Each time 50 liters of water were 
pumped and filtered through bolting silk No. 20. In 1927 the first straight hinge 
oyster larvse were observed on July 14; the spawning probably occurred a day or two 
before when the temperature of the water was about 22° C. A few straight hinge 
larvse, varying in number from 1 to 8 in a sample, were found in daily plankton 
samples collected during the second part of July. On July 29-30 their number 
increased, and from 35 to 80 young larvse were found in some of the samples. This can 
be regarded as an indication of a second spawning, which coincided with a second rise 
of temperature. (See fig. 6.) Small numbers of larvse were found in plankton 
during the first half of August; after August 15 they disappeared completely. 
