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It will be seen that the rates of increase in length of the mussels in these — 
pools show no correspondence to the differences existing among the pools regard- 
ing their surfaces, depths, volumes, maximum temperatures attained, or amount 
of exposure between tides. 
Anchored Float Series. 
An attempt to determine the time at which growth became very slow was 
made. A number of blocks to which measured mussels were attached were set 
out in the middle of September. These were fastened to an anchored float, so 
that they were submerged near the surface. The blocks were taken in at intervals 
of about two weeks after October 18th until December 5th. The results obtained 
(given below) show that after Nov. 4th growth was very slight. 
Date of Average length 
examination of mussels in mm. No. examined 
(When set out 
middle of Sept.) 12 13 
Oct. 18, 719 15.2 20 
Nov. 4, 719 17.4 20 
Nov. 18, 19 ae 23 
Dec. 5, 719 Le, 
SUMMARY. 
1. The greatest rate of growth occurred in mussels constantly submerged 
1 foot from the surface. 
2. The rate of growth in constantly submerged mussels decreases as their 
distance below the surface increases. 
3. The rate of growth of mussels subjected to exposure between tides 
decreases as the amount of exposure increases. 
4. The rate of growth of mussels in tidal pools at various intertidal levels 
varies, but apparently irregularly. 
5. The rate of growth of mussels in intertidal pools and in locations where 
they are subject to intertidal exposure is much less than that in any location 
where they are constantly submerged. 
6. The upper limit at which mussels survive at St. Andrews when subject 
to intertidal exposure is between 19.2 and 21.0 feet above low-water datum, 
depending on the conditions of shelter of their location. 
7. When subjected to intertidal exposure the percentage of mussels surviving 
is much less near the upper limit of survival than at the lower levels. 
8. Growth became exceedingly slow during November in 1919. 
SECTION? Y. 
FACTORS GOVERNING THE DISTRIBUTION. 
The distribution of the mussel beds in the littoral zone at St. Andrews, N.B., 
presents an example of a nice balance among the various factors which affect 
their existence. In Section IV. it was shown clearly that the rate of growth is 
46 
