OF MASSACHUSETTS. 53 



series of attachments and dislodgments, with intervening periods of 

 crawling or swimming. 



The power of byssal fixation is first noticeable at the beginning of the 

 dissoeonch stage, when the young animal is found on eel grass and 

 other objects. The free swimming period of theveliger has just passed 

 and the scallop has entered upon a new existence, that of crawling 

 and attachment. The scallop retains the power of byssal fixation 

 throughout life, but seldom makes use of it after the first year. Scallops 

 fifteen to sixteen months old have been frequently observed fastened to 

 eel grass and to each other, showing that byssal attachment even at this 

 late period in life is by no means uncommon. Perhaps scallops over 

 one year old find little use for the byssus, as, owing to their size, there is 

 less danger of their washing ashore in heavy winds. A twelve-month 

 scallop has been seen to attach itself to the bottom of the aquarium 

 twice within forty-eight hours. 



Observations on the Attachment. — The byssal thread is strong and 

 flexible, as the 6-millimeter scallop when firmly attached can be revolved 

 at least 360° without breaking the strands (Figs. 52-54). 



A curious attachment was noticed in a 2V2-niillimeter scallop on Aug. 

 3, 1908. The scallop was hanging by a byssal thread apparently from 

 the surface of the water. The distal end of the byssus seemed attached 

 to a small bit of mucus on the surface of the water, which was bowed 

 down by the weight of the scallop. The valves of the little animal were 

 apart, the tentacles extended, and the foot was lashing around with a 

 wavy motion. The point of attachment was touched with the tip of a 

 pencil, whereupon the byssus stuck to it so that the scallop could be 

 raised to the surface and towed around the dish. The pencil point was 

 then lowered gently in the water and the scallop remained suspended 

 from the surface as before. This was repeated with the same result. 

 The pencil was thrust through the water until it touched the scallop, 

 which cast off its byssus at once. 



Young scallops swim with the foot extended, and if the foot comes 

 in contact with an object, such as the side of the aquarium, the animal 

 claps the valves rapidly, as if to keep its balance until the foot becomes 

 firmly attached. The movement might be likened to the fluttering of a 

 hen when flying on to a roost. The foot is then drawn in, and the 

 animal remains hanging to that corner of the shell by means of a quickly 

 spun byssus. If the scallop strikes the side of the aquarium with any 

 ofher portion of its body it does not have the power or perhaps the 

 intelligence to swing the body around so that the foot will strike the 

 glass. This observation shows that the scallop of 2 millimeters and over 

 gains its position on the sides of the aquarium as frequently by swim- 

 ming as by the more laborious method of crawling up the sides. 



Value of the Attachment. — The value of the byssus as a protective 

 factor is at once apparent when one considers the rough conditions to 



