21 
having been eaten, while another mussel was removed from the’ grasp of a whelk 
a hole having been partially bored in one valve of the mussel shell. During the 
experiment the round whelks all appeared healthy and moved freely about in ~ 
the tank. It is evidently impossible to form an estimate of the rate at which 
they eat mussels from this experiment. 
The result of the experiment with the starfish is shown in Table VI. 
One of the starfish used in this experiment had been kept in the tank for 
some days without food until the day before the experiment was begun, when it 
TABLE. VII. 
Showing rate at which Mytilus edulis L. was destroyed by Strongylocentrotus droebachiensis 
under laboratory conditions. 
Se | 3 3 & BS Eos eS es ly Ca gee 
ia o one D Last Sbilieeeh ear eae Wot celia : 
eFel=S] 28 | gS |8eh| Sesh) bse é 
hig Sa SO cee. Sea se ewe Oils ace 5 
Zn a |Z 6 ES Ho A we. baer aie 6 2 Zz, 
4 + Sept. 1 9.30 a.m. iat: So ee 88 mussels 
placed in 
aquarium 
4 4 Sept. 2] 9a.m. Paps 12 8.5-10.5 
A 4 Sept. 3] 9.30a.m. 24.5 iF ve 
a 4 Sept. 4] 9a.m. Psa 10 3 
Remaining 
4 4 Sept. 5 | 10 a.m. 25 iba ais a mussels 
removed 
Placed 35 
4 4 Sept. 6] 5 p.m. Siete nie te a mussels in 
tank 
4 4 Sept. 8 3 p.m. 46 6 16.5-25.6 
4 + Sept. 10 fe ? 6 . 
4 4 Sept. 13 | 4 p.m. - 121 2 co 
4 4 Sept. 16 | 4.30 p.m. (CS 3 ¥ 
4 4 Sept. 17 | 2.45 p.m. 10.5 1 - 
*This number of hours was calculated from 3 p.m. Sept. 8th. 
was given four small mussels. On Sept. 4th the starfish were found to have 
moved away from the mussels, which probably accounts for the small number 
eaten from Sept. 8rd to Sept. 4th. By Sept. 6th the mussels were not as numerous 
as formerly in the tank. 
The rate at which the small mussels were destroyed (Aug. 28th-Sept. 6th) 
35 
