The striking thing aljout these seasonal changes in sahnity 
is the suddenness with which the conditions change in 
November and December. This is best seen by an exammation 
of the mean salinities given in Appendix II., or by stud3dng 
the curve of mean salinities throughout the year given in chart 
14. It is this marked change in salinity at the end of the year 
that determines the breeding season of Placuna placenta. At 
the end of December and the beginning of January the water in 
the lake is practically fresh, and spawning takes place about 
the end of January. The spawning season is clearly defined, 
and is not spread over many months as is probably the case in 
the j)earl oyster {Margaritifera vulgaris). 
APPENDIX I. 
Date and Station. 
Date 
and Station. 
September, 1915. 
<5 
December, 1915. 
"^ 
Station 
1 
28-24 
Station 
1 
2 - 67 
Do. 
2 
28-11 
Do. 
2 
2-53 
Do. 
3 
28-06 
Do. 
3 
2-67 
Do. 
4 
28-43 
Do. 
4 
5-49 
Do. 
5 
28-48 
Do. 
5 
4 - 34 
Do. 
6 
27-72 
Do. 
6 
6-65 
Do. 
7 
28-25 
Do. 
7 
6-81 
Do. 
8 
28-30 
Do. 
8 
17-60 
October, 1915. 
January, 1916. 
Station 
1 
28-53 
Station 
1 
11-06 
Do. 
2 
28 • 63 
Do. 
2 
12-16 
Do. 
3 
28-67 
Do. 
3 
13-69 
Do. 
4 
28-34 
Do. 
4 
12-78 
Do. 
5 
27-95 
Do. 
5 
13-48 
Do. 
6 
— 
Do. 
6 
11-14 
Do. 
7 
27-72 
Do. 
7 
14-21 
Do. 
8 
27-62 
Do. 
8 
13-72 
Nove 
rnber, 1915. 
February, 1916. 
Station 
1 
16-66 
Station 
1 
25 • 60 
Do. 
2 
18-66 
Do. 
2 
26-07 
Do. 
3 
18-08 
Do. 
3 
26-55 
Do. 
4 
17-76 
Do. 
4 
24 - 53 
Do. 
5 
21-88 
Do. 
5 
24-25 
Do. 
6 
21-83 
Do. 
6 
24-02 
Do. 
7 
17-08 
Do. 
7 
25-84 
Do. 
8 
17-52 
Do. 
8 
25-23 
