of the Fishery Board for Scotland. 



241 



The mussel sometimes rests a long time with the valves of its shell 

 practically closed, even in clear water. 



I made some experiments on the behaviour of the mussel when exposed 

 to very muddy water. A mussel was left in clear running water until it 

 opened its apertuies fully. A quantity of muddy water was then poured 

 out close to its siphons from a pipette. The fine mud entered by the 

 iuhalent aperture, and immediately thereafter the mussel shut the frill of 

 that part, and sometimes its exhalent siphon and its valves. It then 

 began at once to expel the mud from its branchial chamber by the 

 upper part of its inhalent aperture, the lower part of the same being 

 meantime shut by means of the frills. The mud came out mixed with 

 mucous in the form of small balls sometimes. No mud is allowed to 

 remain in the branchial or mantle chamber of a healthy mussel. The mud, 

 if it enters in suspension, passes on into the gut; if in quantity it is excreted 

 without getting to the mouth. It is, therefore, apparent that an excess 

 of mud is not of advantage to mussels. 



A situation where the mussels could get diatoms and other micro- 

 scopic forms, larvae, etc., with as little mud as possible, should be most 

 favourable for growth. It is possible that they might grow well sus- 

 pended above a sandy bottom. The young attach themselves to wrecks 

 and other objects lying on a sandy beach. 



King thinks that there is more food for the mussel in brackish water 

 than in sea-water, and that the brackish water promotes more rapid 

 growth than sea- water. "Nevertheless, where there is any kind of 

 shelter and freedom from travelling sand, mussels do very well in their 

 native element. A little sand or mud is not of great consequence. The 

 mussels are able when in a body to raise themselves up through it, the 

 more so when a running stream is passing over them." 



The Excreta. — The excreta take the form of a narrow ribbon (fig. 98) ; 

 it is very often discharged in small pieces, but on one occasion it was 

 seen projecting from the exhalent siphon as a band 4 inches in length. 

 In section it is arched, vide fig. 97. 



In a box in which there was only a thin layer of mud, the mussel each 

 day had a little heap of excreta lying near its round end. The water 

 flowing through the box was not muddy to the eye. In the ribbon were 

 found the remains of diatoms; but it consisted mainly of mud. 



Sensitiveness to Shock. — It was noticed on several occasions that 

 on approaching a vessel in which there was a mussel with its inhalent 

 aperture widely open, it would suddenly shut, and close its valves partly; 

 after a little it would shortly open out again. 



Difference in Colour of Mantle, and Fringe, and Siphon. 



In two mussels which spawned in June, the fringe of the mantle was 

 darker in colour than in some of the other mussels near them. 



One large mussel, a male, had the inhalent siphon and the frill of the 

 inhalent a very dark purple colour (tig. 47). 



In another, the inhalent siphon was dark at its base, and had a white 

 distal part ; the frill of the inhalent had a dark amber base with a lighter 

 amber colour on the free border (fig. 40). Another, which had prin- 

 cipally an amber colour in these parts, had the whole of the anal siphon dark. 



The frills are sometimes dark to the tip, sometimes distinctly lighter 

 thdre. The inhalent siphons are sometimes tipped with white or wholly 

 white, amber, or purple. 



Some shelled mussels were examined in order to see if the difference 

 in colouring was sexual. But no definite rule was made oat. 



