Growth-rate of Mussels. 201 



young stages from various scattered observations. For instance, 

 specimens reared from fertilized eggs, in 12 days were then 

 O134! millimetres ; though they lived for 40 days they made 

 no further progress in development (Wilson). Other samples 

 0'27 mm. to O45 mm. have been assumed to be about 1 month 

 old (Johnstone). Some examples J inch long, which appeared 

 in the well of a Tees steam-dredger, were supposed to be 

 about 2 months old but queried by Mclntosh. A series 

 each under J inch obtained from barrel buoys at St. Andrews 

 were conjectured to be 5 months old. Mussels on "Roosebeck" 

 Scars (near Piel Laboratory) are known to have grown f of 

 an inch in 5 months (Scott). At Montrose it is reckoned 

 that seed-mussels on the best ground attain 2 inches length in 

 3 years, in other parts of the beds up to 5 years is required 

 (Fullarton). 



According to mussel culture in the Thames estuary, the 

 smallest sized laid in February and March are from 1 to 2 

 inches long, and are reckoned to be about 1 to If years of 

 age. When 6 months on the bed, that is to say from 1J to 



2 years old, they as a rule will be about If to 2 inches in 

 length, some being over. The very biggest of not less than 2| 

 inches will then be fit for market. At 3 to 3f years of age 

 they may be nigh 3 inches in length, if in low-lying ground 

 and covered by water. If inclement weather their growth 

 is not so quick, but given an extra spell of warmth, with 

 favourable tides, this stimulates them with a spurt. Sup- 

 posing the mussel's development is divided into four stages, 

 the first makes slow progress in growth, the second and third 

 are much accelerated, whilst in the fourth, nigh full-grown, 

 there is, other things being equal, retardation of increase in 

 dimensions. 



As to the mussels on sale at Billingsgate, their average 

 sizes on the stalls generally are from 2| to 3 inches. The 

 former usually predominate ; a few only 2 inches in length 

 find their way to the dealer among the others. Larger than 



3 inches are a rarity. The big Horse Mussel (Mytilus modiolus) 



