23 
set was placed in tidal pools, the pools being situated at different intertidal 
levels. During these experiments it was found necessary, owing to the depreda- 
tions of Purpura lapillus, to protect the mussels (by means of wire netting) on 
the blocks forming the series on the wharf up to a level of 17.6 feet above low- 
water datum. Similarly it was found necessary to-protect the mussels in the 
lower six tidal pools, 7.e., those in the zone whose upper limit was 17.6 feet above 
low-water datum. ; 
TABLE VIII. 
Showing rate of increase in length of Mytilus edulis L. during breakwater series experiment 
in 1919. 
Block 1 2 3 4 5 
Depth ite etDElOW. SULLACE He. tee eles Scr aes | 1 2 3 6 9 
No. Onublockuwhentset outs iily.See saeco 69 64 50 56 Pee 
No. OuplOGk eA onl a sea ouster ee orto. erent a oul 38 44 18 33 aa 
Pocontiee Onkblock, AM cara em rare atavsh. caer scrote + SYS (0) |b Cotsh, 0 36 | 58:8 ee 
No. a blacks Sepi-7 Ohern Se oieess se wi, Fe ae hater che, heise 21 29 17 28 oe 
ee ri icena: sare oes 30.4 | 44.1 34 | 51.8 56.3 
rece. length in mm. when set out July 8......... 11 11 10.5 10.5 Pio 
(ee TAIT PAM OAR. Arcot Teietate« trakece s60| LOO 16.3 16.3 15.6 eon. 
ee: increase in length in mm. July 8-Aug. 4, 2.e., A iy 
NN SIRO S one hn 3 oko es/s Need oe Oe oe e ae 5.6 5.2 5.8 5.1 4.5 
is. Coe eee 10 13 6 5 Lee 
ee increase in length in mm. per day, July 8- aan 
ER AED eR ra Ph la actA 8) = dh « AS roar gaol. be 0.21 | 0.19.| 0.22 | 0.19 | 0.56 
A fenonhsin Mme pbs Aer - oh ass kee oe Bot Pee 2oe ae 2osOne Zool i 
oe increase in length in mm. July 8-Sept. 9, 2.e., ‘aie 
Mi Gea Sta nw fe0s oce sd Si he ees eae Lege Sh 16.2 14.7 14.5 13.6 oO 
aan examined one Ones a Poca 2 eke 12 15 ea 18 ; eg 
Average increase in length in mm. per day, July 8- 
SS) o1Fs 1S eo ete Ce ae CPR ne ase are cee ers ae Tee 0.25 =| O:24 4) 02232, hO.2t story, 
Breakwater—Series. 
In this experiment five blocks (Nos. 1, 2, 38, 4 and 5), to which measured 
mussels were attached, were nailed crosswise to a scantling which was fastened 
to the floating breakwater at the Biological Station in such a manner that the 
37 
