240 Part III. — Twenty -fifth Annual Report 



Some rausseU taken off the wall of the big pond were put into a fish- 

 box, which was sunk to the bottom near the inlet valve. The bunches 

 of mussels were clean when they were put in. In the Spring (April), 

 after having been in the pond since the previous November, that is, for a 

 period of live months, the box was examined The mussels were now 

 found to be embedded in a thick bed of slimy adhesive mud. The 

 bottom of the pond had comparatively little mud on it at that part. The 

 mussels had gradually collected the mud from the water that passed 

 through the box, and when they passed it out in the form of excreta it 

 had been retained there. In the bottom of the mud some of the mussels 

 had been choked, the empty shells alone remaining. These had been 

 bound by the other mussels in the bunch, and had not been able to free 

 themselves. Other individuals had grown. 



Some bunches of these mussels were washed and put into a floating 

 box, in which the mussels were submerged about six inches, and were 

 three to four feet above the bottom of the pond. On July 19, when they 

 were examined, they were found to have collected a fine gi'easy coherent 

 mud in a corner of the box where there was no opening in the bottom 

 to permit of the excreted mud escaping, as it could do in other parts of 

 the box. This indicates their capacity for collecting mud. The box was 

 floating in a part of the pond which was shaded by the floor of the tank 

 house. The mussels were judged by an authority to be of good quality. 

 The surface of the box was thickly coated with barnacles (Balanus), 

 especially on the side facing the inlet of the pond. 



In addition to the accumulation of mud, the mussels in the aquaria 

 in the Laboratory suffered under another unfavourable condition. 

 Being exposed to the liglit, they were in the summer months coated more 

 or less with a growth of filamentous algse, which also lined the interior of 

 the aquarium. This prevented them feeding to their full extent. Fig. 

 56 shows a mussel fully opened. 



The mussels were in the quality of their soft parts in good condition 

 generally, but they had not grown. The majority had survived. The 

 permanent conditions, salinity of the water, and quantity of food were 

 suitable ; the latter was possibly not specially favourable. The local and 

 temporary condition, viz., accumulation of mud and algoid growth, were 

 unfavourable. They were never left dry, so that tliey had not this 

 recognised interference with growth to contend with. The mussels were 

 put into floating trays to escape the mud, but this arrangement intensified, 

 if anything, the growth of the algae, in that way neutralising the advan- 

 tage accruing from the freedom from mud. 



A sufficiently strong current running over the mussels, or a current 

 interrupted and reversed, such as is afforded by the tide, might have 

 prevented the accumulation of the mud. It would also appear to be an 

 advantage that the mussels be kept away from a strong light, by being 

 well submerged, where these growths would not develop. 



Feeding. — When the apertures of a mussel are wide open (fig. 56), 

 a large quantity of water is taken in, and the water issuing by the anal 

 siphon forms a very considerable current, as has been noticed when the 

 mussel was near the surface. 



When a mussel is surrounded by a thick layer of mud, or with 

 filamentous algse, it does not open its inhalent aperture freely, and 

 therefore cannot obtain a full supply of food. Even although there 

 is a considerable quantity of mud in suspension in the water, that does 

 not seem to prevent the mussel opening its inhalent aperture to the 

 fullest extent. Diatoms, foraminifera, and spores Jiave been found in 

 the mud in the aquaria. 



