of the Fishery Board for Scotland. 



289 



the reach of a continuous supply of food. They may justly be regarded 

 as mussels that have ceased growing and are only existing." At the end 

 of five months they had grown |-inch, and instead of being thin and 

 watery, they were in fine condition. Six months after transplanting 

 some mussels that originally measured lj-inch were found to have added 

 | -inch to their length, while the mussels that had been left in the 

 original bed had increased 5-inch in the same period. The authors drew 

 attention to the fact that it is comparatively easy to detect a mussel that 

 has been transplanted. The new part of the shell is black and clean, 

 in contradistinction to the slatey-coloured originally stunted shell. 

 Vide fig. 105, which is a drawing of a transplanted mussel from 

 St. Andrews, natural size. A-B represents the original seed ; B-C 

 increase in the shell after transplanting. 



The mussel that grows to a full size in the deep without transplanting 

 has a uniform shell, darker and cleaner. The barna.cles (Balanus) do not 

 settle on mussels in the deep to any considerable extent. 



The Mussels in the Laboratory and Pond. — None of the mussels 

 in the Laboratory grow to any extent. They were supplied through the 

 upper reservoir from the inlet pipe of the big pond. In the pond a large 

 quantity of mixed mussels were got. They were attached in a broad 

 row on the side of the pond about a foot from the bottom, and three feet 

 below the surface of the water at one part, and six feet below it at another. 



They were most thickly packed near the inlet of the pond, and extended 

 along one side, across the end, becoming gradually fewer. Practically 

 none were found on the third side. It is remarkable that they were not 

 spread all over the pond. The barnacles (Balanus) were spread all over 

 the sides right up to the surface of the water. 



The row of mussels coincided with the line that the current flowing into 

 the tank takes. A wire-netting screen inside the tank intercepted the 

 current to some extent, and the mussels attached themselves to it in 

 quantity. On one occasion when the screen was removed the greater 

 part was choked with a sheet of mussels. The mussels in the pond were 

 of all sizes up to 2| inches and they were fat. Some baskets of them 

 were tried as bait by the local fishermen, and they were found to do just 

 as well as the mussels they were using. 



Mussels were found in the upper reservoir tank up to a size of 1J- 

 inch, and when examined in November they showed thin, ill-conditioned 

 animals. This seems to indicate that the water-supply was poor in 

 suitable food, generally so for part of the year. 



The pond itself would probably breed its own supply of diatoms and 

 other food, and that may account for the fatness of the mussels there. 



The water supplied to the Laboratory contained, no doubt, at certain 

 times of the year a good supply of suitable food, but probably on the 

 whole the quantity of food was not abundant. That will account in 

 some measure for the fact that the mussels grew so little. But there 

 were other mechanical drawbacks. The vessels in which the mussels 

 were kept soon had a deposit of fine mud on the bottom. This was in 

 part excreta ; the mussel took in the fine mud that entered in suspension 

 in the water supply, and which, if not arrested by the mussel, would have 

 largely passed out by the overflow, and excreted it in a compact ribbon 

 form. It was now much heavier, and lay on the bottom close to the 

 mussel. This would tend to arrest fine mud. 



When the mud accumulated to the depth of possibly half-an-inch, the 

 mussel sometimes moved about to free itself from it. It might simply 

 shift its position on the bottom, showing its movement by the track it 

 left in the mud, or it might climb up the side of the vessel. 



