28 
It will be observed that in the second south pile wharf series experiment, the 
mussels survived at 21 feet above low-water datum, while in the first south pile 
wharf series experiment, the highest-level at which they survived was 19.2 feet 
above low-water datum. This was probably due to the fact that during the 
second experiment the weather was cooler than during the earlier one. The 
second set was, therefore, not exposed to as high a temperature when uncovered 
as the first set. It will be noted also that the number surviving shows a decided 
tendency to decrease as the exposure to which the mussels were subjected in- 
creases. The irregularities occurring in the percentage, surviving at the higher 
levels, is probably due to slight differences in the various blocks favouring attach- 
ment and protection for the mussels. It will be seen, also, that the rate of growth 
shows a tendency to be higher at the lower levels than at the higher ones. While 
this tendency is evident, it is subject to several irregularities. Since the rate for 
block ‘‘G3”’ is based on only three mussels is of little value and is probably too 
high. 
Unfortunately, owimg to some misunderstanding of instructions, the second 
below-beams-wharf series was not preserved at the same time as the second 
south-pile-wharf series, but instead was left until November 21st. Consequently 
it is impossible to compare the rate of growth at the various levels as had been 
intended. The rate of growth per day is not very significant either, since growth 
(as will be shown later) was at most very slow during November. The results 
of the experiment are given in Table XIII. 
TABLE XIII. 
Showing rate of increase in length of Mytilus edulis L. during second below beams wharf 
series experiment in 1919. . 
Block AA| B4i! C4) D4 | B4) F4G4 7 H4 14 
Height in feet above low water datum... sor 11.0 12.6 14.1 15.8 17.4 19.1 21 22.6 
ie length in mm. when set out ae ea ee bos ce 
PAU SOS eer 3 SG she theeteers see ees 10 10 10 10 10 10 10 10 10 
Nutiber BEL OME ais foo ere aie te Stee 56 91 70. 95 “on 95 72 76 “67, 
ae recovered Nov. 21, '19........ 35° 55 “36. 22 me 9 ey 4 wee 
eee. recovered Nov. 21, ’19...... 62.5 60.4 51.4 23.1 15 9.5 ar 5.3 a 
Aas length in mm. Nov. 21........ 13.9 13-7 13.0 13-2 10.7 il & =. Theil a 
Average increase in length in mm. from 
Aug-19 to Nev..2! #.¢., m'94 days... 1) 3.9)! 3.7 3.0) 82) | k0n a deat eee ee 
It will be seen that in this series the highest level at which the mussels 
survived was 21 feet above low-water datum, 7.e., at the upper limit or survival 
in the second south-pile-wharf series experiment, and in the first below-beams- 
wharf series experiment. 
42 
