INVESTIGATION OP OYSTER SPAWNING, ETC., MILPORD, CONN. 489 



surface with which it is brought in contact. The larva then ceases swimming and 

 crawls over the surface by means of its long muscular foot, at the same time laying 

 down the byssus behind it. After crawling about for a short time, the larva comes 

 to a standstill, ejects a quantity of cement on its left side, and quickly brings the 

 lower or left valve into contact with the cement-covered surface. The foot is used 

 in bringing the shell in contact with the substratum and holds it in position for 

 about one minute. This short interval of time is all that is necessary for complete 

 hardening of the cement and setting of the oyster larva. Immediately following 

 fixation, a metamorphosis occurs, and the larva develops into a spat with organs 

 similar in structure to those of the adult oyster. At this time the newly formed 

 spat is cf the same size as the fully developed larva and measures 0.33 of a milli- 

 meter, or approximately one seventy-fifth of an inch through its greatest diameter. 

 In shape it closely resembles a hard clam and has an amber-colored, irridescent shell, 

 near the center of which can be seen a small, deeply pigmented spot. The spat 

 grows rapidly and in one week is over five times its original length and in two weeks 

 over twenty times, when it reaches a length of about 7 millimeters, or one-fourth 

 inch. Spat of this size cau easily be seen on the shells and other collectors and were 

 the smallest to be counted in the field observations with regard to the number at- 

 tached on a given area of surface. 



In the studies of the distribution of setting, various types of spat collectors were 

 used, such as tiles, brush, tar paper, and containers filled with oyster, clam, scallop, 

 and mussel shells. The collectors were arranged so as to cover the entire zone from 

 the bottom of the channel to high-water mark, a vertical distance of approximately 

 17 feet, of which the upper 5 to 9 feet are exposed by the tides. In addition, four 

 ropes, to which tiles were attached, were suspended from an oyster float anchored 

 near the beds. 



Setting in Milford Harbor has been observed to occur from July 20 to September 

 1 , but is generally most intensive during August, the peak occurring about the middle' 

 of the month. It was found that setting was not a continuous process, as there 

 occurred definite periods of setting that followed spawning by about two weeks. The 

 first set that occurs is early and extremely fight and is followed by a heavy and final 

 set about 8 or 10 days later. For example, in 1925 there were 10 to 15 spat per shell 

 at Station 3 in the light set and from 150 to 250 spat per shell in the heavy set. An 

 examination of the shell samples taken up daily showed that the majority of the larvae 

 from a single spawning became attached within a day or two of each other. In 

 1926 the heavy set occurred on August 16, which is representative of the average 

 time of setting for this region. In 1925 spawning and setting occurred two weeks 

 earlier than usual, and the heavy set was observed on July 29. 



The number of spat produced in the harbor each year varied considerably, 

 though the size of the spawning bed was virtually the same in each instance. It 

 was found that the intensity of setting could be clearly correlated with the quantity 

 of spawn in the oysters and the early water temperatures. In 1925, when the tem- 

 perature was above normal and the oysters contained a large amount of spawn, 

 setting was heaviest, and an average of 15,000 spat per bushel of shells was collected. 

 In 1926 and 1927 we had the other extreme — that is, water temperatures below nor- 

 mal and a small amount of spawn in each oyster, with the result that the average 



