RESUME OF THE STAGES OF DEVELOPMENT 85 



the fact that I was looking for spat every day in the same manner, and that 

 up to that date I had found none, but afterwards I found many both on 

 glass strips and on shells, and they were all extremely small. In 1909 the 

 first spat I captured was on the 19th August, taken at the same place and 

 in the same manner. 



The number of spat is small at first, rising to a maximum, and then 

 falling. At first it is necessary to examine many shells to find a single 

 minute spat. In a week or two it may be possible to find one, two, or 

 three on almost every shell. I have never seen anything like such numbers 

 as Ryder, Rice, Brooks, Nelson, Grave and others have described and 

 figured. 



Ryder (1883) : " As many as 25 young oysters might have been counted on a surface 

 of one square inch," (on wooden buoys taken up early in July near Woods Holl), and 

 again " more than 100 oysters on a single shell." 



Rice (1885) figured the inside of an old oyster valve with 165 spat attached. 



Brooks (1905) figured an oyster shell bearing 150 spat. 



The rate of growth of a young spat has been observed by Jackson 

 (1890, Plate XXIV, fig. 3). He caught a spat on glass, so recently at- 

 tached that there was no additional growth to the larval shell, and kept 

 it alive in a beaker of sea-water for four days. In three days it almost 

 doubled its height. 



An experiment of my own at Malpeque in 1904, in which the spat 

 comes next in size to that of Jackson, shows one half the rate of growth. 

 This spat was procured on the afternoon of August 31st at Ram island, 

 about six miles from the station, and measured at 5 p.m. -861 x -953 mm. 

 in height and length. It was kept under the arch of the wharf until the 

 afternoon of September 1st and measured again, but it showed no in- 

 crease in size. It was then taken to Ram island and placed under its 

 original conditions, but in a crock, and at 4 p.m. September 7th, it measured 

 1-276 x 1*260 mm. It was kept in running sea-water until 5 p.m. of the 

 8th, and then put under the arch of the wharf until the morning of the 9th, 

 when it was again taken to Ram island. It did not grow either in the 

 running water or under the arch of the wharf, where there is at times con- 

 siderable tidal current. On the forenoon of the 16th it was again brought 

 in and measured 1-753 x 1-661 mm. It would appear that the spat did not 

 become immediately accommodated to new conditions after being dis- 

 turbed. As the measuring was made at intervals of six and seven days 

 it is impossible to say how much of the time was taken up in getting accom- 

 modated and how much in actual growth. If we start with the size of the 

 largest larval shell, -369 mm., and, taking Jackson's results, add one- 

 third for each day's growth, the heights would be -492 (one day spat), -615 

 (two day), -738 (three day), -861 (which was the height of my spat at 

 the beginning), -984, 1-107, 1-230 (approximately the height of my spat 

 after six days growth), 1-353, 1-476, 1-599, 1-722 (approximately the 



