St. Andrews Marine Laboratory. 469 



young mussels when they are settling in autumn on the 

 blades of the seaweeds or on the rocks fringing St. Andrews 

 Bay ; and it is possible the minute young mollusks then 

 attach themselves to the gills and grow apace with the 

 young fish, the relative sizes of the two species being a 

 feature of considerable interest. In these and other instances 

 which need not at present be multiplied the young mussels 

 fix themselves on sites well adapted for both aeration and food. 

 It is, again, an erroneous view (not altogether confined to 

 the unscientific observer) to suppose that because mussels of 

 considerable size are found on a particular site, e. g. a ship's 

 bottom, this indicates that since last " cleaning " they have 

 grown from their pelagic stage to the, it may be, very con- 

 siderable size in question. As Mr. Wilson has shown^ it is 

 a well-known fact that mussels can leave their sites and fix 

 themselves to new ones by a fresh secretion of the byssus. 

 Indeed, in France they are often artificially torn off and 

 placed in slender netted bags for attachment to poles or 

 wattles. Before the meshes of the net give way they are 

 again firmly fixed. All that is required tlierefore in the case 

 mentioned is that the ship settle down on the mussels in 

 the harbour, detach some, and for these again to fix themselves 

 afresh to the ship's planks. If in addition to these the 

 timbers are already coated with a series of small forms whose 

 fixation dates from the pelagic period, a somewhat complex 

 condition is presented. 



3. On a Post-larval Pleuronectid [Turhot ?) . 



In the large mid- water net at 3| fathoms over sandy 

 ground off the estuary of the Eden, on the 22nd August, a 

 post-larval Pleuronectid measuring 5 millim. was obtained. 

 Its coloration was so striking tliat at first sight it seemed to 

 be provided with a series of dorsal papillae or processes, the 

 first of which projected from the occiput. This appearance, 

 however, was only due to the boldness of the pigment and 

 the e:^treme translucency of the marginal fin. The latter 

 stretched from the tip of the snout to the tail, which was 

 somewhat oblique from the dorsal bend of the notochord, and 

 again along the ventral line forward to the abdominal pro- 

 jection. 



The fish had reached the stage at which the Pleuronectid 

 character was evidenced by the great ventral increase of the. 

 abdominal region and by the depth of the body generally, 

 while the upward bend of the notochord and the slight deve- 

 lopment of the hypural elements were also noteworthy. The 



