( 14 ) 
Chrowih Rate {Linear). 
In Appendix I. an analysis of the linear dimensions (short 
diameter) of the different age groups of oysters, as Avell as the 
mean measurements, are given. In Appendix III., these 
mean measurements are arranged in order of age. In Fig. 1 
these mean measurements are plotted, and thus a very reliable 
curve of the mean growth rate can be obtained. This curve, 
which gives the gro^vth rate over seven years, is instructive. 
It will be seen that Placuna placenta attains a growth of 1 70 mm 
(short diameter) at the begmnmg of the eighth year. Nearly 
half this groAvth takes place in the first twelve months, so that 
the curve is very steep at first and becomes increasingly 
flatter as the mollusc grows older. The actual increase in the 
seventh year is only 10 mm., compared with 75 mm. in the 
first year. 
Growth Rate {Weight). 
Details of the weights of the different age groups at each 
inspection are given in Appendix II. From the mean measure- 
ments thus obtained we are able to give the mean measure- 
ments of all groups of oysters in order of age {vide Appendix III . ) . 
In Fig. 2 these mean measurements are plotted, and a curve 
of the mean groAVth is obtained. This curve is the reverse 
of that obtained in the case of the linear growth, that is to 
say, the rate of growth increases as the age increases. Thus, 
the weight increases by 20 grms. in the first year, by 50 grms. in 
the fourth year, and by 85 grms. in the seventh year, the mean 
weight at the beginning of the eighth year being 360 grs. 
From these two curves the followuig mean measurements 
for linear growth and weight are given for every six months 
up to the beginning of the eight year : — 
Short „r . , . 
Diameter. ^^^^S^*- 
(mm.) Grms. 
,-,. , ,;• f Februarv . . — . . — 
tirst Year • • a i. " en o 
l^ August . . 50 . . 8 
Second Year 
f Februarv . . 75 . . 20 
l^ August ' . . 90 . . 35 
