244 Part III. — Twenty -fifth Annual Report 



the algse were tending to retain the fseces in close proximity to the 

 mussel. 



Several of the mussels, though set originally on the bottom, climbed up 

 the sides. 



Mussels, if placed on their back iu water, very soon turn back up, 

 usually within 24 hours. Some mussels, 2| inches long, were put on 

 the bottom of a box filled with water, with the hinge down. Certain of 

 them showed some activity in turning back up ; they had done so by 

 next day. They put out the foot, round the shell and down to the 

 bottom of the box, and, taking hold with the tip of the foot, they 

 pull themselves round till they lie back up. One moved a good 

 bit out of the run of the current which ran over the bottom of the box. 

 Others attached themselves where they happened to have been set down. 

 On July 12 one in a glass aquarium had not yet succeeded in turning 

 over. It attached some threads to its own shell, and a few days later 

 some threads were fastened to the bottom. A day or two after it was 

 seen to be back up. It had been back down for nine days. 



Some mussels were put into a box, and 18 hours afterwards they were 

 all attached by byssus threads. Another rose up on end and attached 

 itself with' a large number of threads in the same time (fig. 81). 



Mussels Trying to Keep in the Water by Slackening the Byssus. — Some 

 small mussels, about 1^ inches long, were attached up on the side of a 

 box filled with water. When the water was being let out the mussels, 

 as they were being left by the water, slackened their byssi (fig. 8'i) 

 in order to keep themselves in the water; but when, having come to the 

 end of their tether, they found the water still receding, they hauled in 

 again and lifted themselves up tight against the side of the box 

 (fig. 83 ) 



Movement of the Modiolus modiolus. — On March 22 some Modiolus 

 were put into a tank. They were very slow in attaching themselves. 

 By April 4th one of them had attached itself by some very long threads, 

 had cast its byssus and re-attached itself. Later, there were several of 

 these cast byssi, some of them having only a few hairs. The Modiolus 

 therefore appears to behave exactly similarly in the matter of movement 

 to the Mytilus edulis. It does not appear to be so active, however. 



The Anatomy of the Byssus and Foot. 



The most important publication on the subject of the byssus with 

 which I am acquainted is Tullberg's. He gives drawings of sections of 

 the byssus-pit and foot, and also of the septa of the pit and various 

 glandular elements. From Tullberg's extracts it is clear that Miiller's 

 theory regarding the ruode of formation of the byssus is wrong, 

 in parts at least, as Tullberg maintains. I have not been able to consult 

 Reichel's paper, "Ueber die Bildung des Byssus der Lamellibranchiaten, 

 Zool. Beitrdge, Schneider. 2 Bd., 1888." 



Lang summarises the description thus : — " The byssus can generally be 

 thrown off or replaced by a new one, and many forms can move about on a 

 smooth perpendicular pane of glass by means of alternate attachment and 

 rejection of portions of the byssus applied by means of the foot. [It is 

 doubtful if a portion of the byssus can be rejected, unless merely the 

 snapping of threads is here meant by the expression.] The byssus cavity 

 is divided into narrow shelves by numerous folds which project from each 

 side into its lumer. A septum descending from its roof further divides 

 it into two lateral parts. The byssus secretion is yielded partly by the 



