19 
The rate at which the mussels were destroyed from September 2nd, 2 p.m., 
till September 8th, 3 p.m., was 0.9 mussels per Purpura per 24 hours. The rate 
at which they were destroyed from September 8th, 3 p.m., till September 19th, 
9.30 a.m., was 0.9 mussels per Purpura per 24 hours. 
The experiment with the common whelk was unsuccessful. Five whelks 
were placed in a small aquarium with a few medium sized mussels (6 or 8 mussels 
of from 2 cm. to 2.5 cm. in length) on Aug. 29th. None of the mussels were 
eaten from that time until Sept. 19th (z.e., during 21 days) when the experiment 
TABLE V. 
Showing rate at which Mytilus edulis L. was destroyed by Purpura lapillus under laboratory 
conditions. 
n VY 
; Ee ad a= 
bh < ra =!6 aD S 
BES ea tis see oes Re) a } & 8 Sa «(OC me <= 
as|o8| . ems | Paes eee, in|) oS 
eee ome tee Stee lltsoeree | ewe cane ls eco e Z 
pees ea ea” Soe ile. aaa ees em |e ats g 
6.s1o°| So 5 3 oO Bea Sea Sys fs a8 2 o ° 
ZEW A you =e) FO Zao ZY eS Vee a Zz 
19 ce Aug. 30 | 3 p.m 
19 0 | Aug. 31 | 3 p.m. 24 
19 1 | Sept. 2.) 2 p.m: 47 1 8.5-10.5 
19 1 Sept. 5 | 9 a‘m. 67 1 i 
19 2 Sept. 6 | 9 a.m. 24 4 S 
19 4 | Sept. 8 | 3 p.m. 54 9 ic removed 
15 Purpura 
ft 4 | Sept. 8 | 3.05 p.m. 
4 2 | Sept. 10 | 3 p.m. 48 4 8.5-10.5 
4 2 | Sept. 13 ? ? 6 %s 
Ane: i: Sept. 16 | 5 p.m. 145* 3 cs 
4 2 | Sept. 19 | 9:30 a.m. 64.5 6 _ 
*This number of hours oe calculated from 3 p.m. Sept. 10th. 
was ended. From Sept. 7th-13th one of the whelks died; with this exception 
the whelks and mussels appeared healthy during the experiment. The whelks 
were active and moved freely about in the aquarium. 
The experiment with the round whelk was begun Sept. 12th and ended 
Sept. 19th. A number of mussels ranging in size from 8.5 mm. to 20.1 mm. 
length were placed in a large wooden tank with 8 or 10 round whelks. On 
Sept. 15th one mussel shell was removed, the animal having fallen a victim to a 
round whelk. On Sept. 19th two other shells were removed, the animals within 
33 
