25. 
depth from the surface increases. It will be noted, too, that the percentage 
surviving September 9th on the block 1.foot from the surface was noticeably 
less than on the blocks at greater depths. The greater wave action at the 
surface probably accounts for this. 
Anchored Pole Series. 
In this experiment ten blocks (Nos. 11 to 20), to which measured mussels 
were attached, were nailed lengthwise along a pole. This pole was anchored in 
the cove at the Biological Station so as to float upright ten feet from the bottom. 
It was so located that the mussels were never exposed even at low water. There- 
fore the mussels on this pole were at a constantly varying depth from the surface. 
The results from this experiment are shown in Table IX. 
Considering the results of the examination of material taken September 
15th it will be seen that the greatest rate of incréase in length occurred at the 
upper end of the pole and that the rate of increase in length shows a tendency 
to decrease as the lower end of the pole is approached. It will be noted that 
there is a considerable irregularity in the results when considered with reference 
to this tendency. This is probably largely due to the fact that many of the 
mussels moved from their original positions on the blocks and wedged themselves 
between the blocks and the pole, thus obtaining more sheltered positions. It 
was impossible when collecting the mussels for examination to make note of 
these individual differences. It will be observed that the rate of increase in 
length at the upper end of the-pole, viz., 0.17 mm. increase in length per day, 
corresponds with that at 9 feet from the surface in the breakwater series Sep- 
tember 9th. 
The material collected October 18th unfortunately represents only a portion 
of this series. It will be seen that it indicates that the rate of growth from 
September 15th to October 18th was distinctly slower on the whole than from 
August 4th to September 15th. The fact that the increase in length of the 
mussels examined from the upper block was less October 18th than that of those 
examined September 15th may be due to the small numbers examined September 
15th. From the limited data available it is impossible to judge whether the 
increased rate of increase in length observed as the depth from the surface 
increases is significant or not. 
Wharf Series. 
In this experiment two sets of eleven blocks (Nos. Al, B1, to K1, and Nos. 
A2, B2 to K2) on which measured mussels were attached were put out in two 
vertical series July 4th. The blocks used were pieces of weathered shingles 
about 2.5 inches wide and 10 inches long. One set of blocks (known as the south 
pile wharf series) was fastened on one of the south piles of the wharf of the 
Biological Station. In this location they were constantly exposed to direct 
sunlight during the day. The other set (known as the below beams wharf 
series) was fastened below the beams on the east side of the wharf. In this 
situation the whole series was constantly shaded. Corresponding members of 
each series were placed at the same level above low-water datum. The results 
of the experiment are shown in Tables X. and XI. 
39 
