F. S. Wright 



139 



results obtained are not of great value. Other cages, more carefully 

 constructed, were placed in the river at Aberdovey, and have not yet 

 been recovered. It is feared that a recent "creep" of the foreshore may 

 have buried them. 



Despite these setbacks, however, some valuable data has been amassed 

 with regard to the growth of Mytilus during the close season. Upon 

 removal from the poor areas (seed beds), the transplanted mussels make 

 such rapid shell, as well as flesh growth, that usually a distinct ridge 

 is formed on the shell, which marks off its older portion from the newer 

 growth. When removed from a poor to a better situation, this mark 

 is so definite and unmistakable, that it is impossible to doubt its 

 meaning (Fig. 3). At the commencement of the fishing season {i.e. after 

 the transplanted mussels had spent about seven months on the fishing 

 beds), I examined a large number of individuals, which, from certain 

 unmistakable indications, had been brought from the poorer situations. 

 The average increase in length made by a two-inch mussel in this time 

 was found to be rather more than half an inch (actually jV')- 



Growth Rate of the Sea Mussel. 



NoAv let US consider the increase in cubic content which this gro\Yth 

 in length represents, — reckoning the latter at half an inch. The fol- 

 lowing figures were obtained by placing in water a large number of 

 individuals (sometimes singly, sometimes more than one), in a partially 

 filled measuring glass graduated in cubic centimetres. In each case, 

 the valves were carefully tied with cotton to keep them in apposition, 

 as any water entering them would have resulted in too low a reading. 

 A number of shells were also treated in a similar manner, and the 

 readings for them, being deducted from the total mass including the 

 shells, give the correct figures for the valve content. This of course 

 includes flesh, air, water, etc. 



Ami. Biol. IV 10 



