88 INLAND FISHERIES. 



surrounded by so dense a feltwork of roots from the marsli vege- 

 tation tliat it would seem entirely imjDossible that the adult animal 

 could remove itself. It is a mystery how the young- could ever 

 force its way into such material. 



FIXATION IN THE BUREOW. 



A peculiar habit, the utility of which is very evident, is the spin- 

 ning of the bj'ssus by the small clam as soon as it has succeeded 

 in covering itself in the sand. As has just been stated, the small 

 individuals bury themselves, and again appear upon the surface, 

 and this is repeated several times. But whenever the creature 

 goes into the sand, it apparently at once proceeds to pour out the 

 secretion which forms the byssus thread, and attaches itself more or 

 less firmly by this means. Figure 3 represents a clam with a shell 

 2f^^ millimeters long which has been removed from its burrow. 

 The single byssus thread (b) is seen to branch, the ends of the 

 liranches being attached to three sand grains (s. g.). Actually the 

 number of sand grains and pebbles to which attachment is made 

 is usually greater than represented. The extremity of the thread 

 which is fastened to the foreign body is considerably widened, as 

 shown in the figure. The character of the thread is the same, 

 whether the creature is attached to several sand grains, or to a 

 single filament of Enteromoiylia or to other bodies. Figure 2 

 represents a very small individual, i\ of a millimeter in length 

 (drawn on a larger scale than Figure 3), which was attached by 

 several branches of the byssus to one short seaweed filament. 



In coming out of the burrow and moving to a new locality, the 

 byssus is cast off at the gland in the foot and left behind, and a 

 new one is constructed at the next descent. This is accomplished 

 in the space of a few minutes. Clams, from the smallest Avhich 

 are able to cover themselves in the sand, to those at least 13 milli- 

 meters in length, exhibit this peculiar habit of forming a byssus 

 in the burrow. How much longer the byssal organ remains in 

 functional activity, and when it begins to atrophy, I have not 

 determined. 



