342 Our Food Mollusks 



ably even in the late embryonic swimming stage a byssus 

 gland is developed at its base and becomes functional, for 

 very small individuals hardly more developed than the 

 late swimming forms, have been found attached to float- 

 ing objects, and Mr. Belding has witnessed somewhat 

 older individuals, about one millimeter in diameter, 

 swimming at the surface of the water with foot ex- 

 tended, and has seen them attach by the sucker-like end 

 of the foot on coming in contact with the sides of the 

 aquarium. A moment later they were seen to be at- 

 tached by byssus threads. 



By a groove on its under surface, the foot forms this 

 thread from the byssus secretion, and attaches its end. 

 While at first the thread is single, the number of strands 

 in the organ increases as the animal grows, and it be- 

 comes a firm tether. Figure 67 shows its appearance 

 and relative size in an individual about half an inch in 

 diameter. The deep notch shown in the shell where its 

 lobe-like wing joins the main body, is for the accom- 

 modation of the attached byssus. This bundle of threads 

 is cast off at will from its proximal end, and new 

 threads are formed when needed. From time to time 

 attachment occurs during the greater part of the scallop's 

 life, though infrequently in full-grown individuals. 



It should be observed that the habit of very early 

 byssus attachment seems to have a direct bearing on the 

 distribution of scallops, for it accounts for the fact that 

 they are so frequently found in grass-covered bottoms. 

 Usually in the early summer great numbers appear at- 

 tached to the blades of eel-grass with which they may 

 have come in contact while swimming, and to which they 

 have fastened, as to the glass of the aquarium. The long 

 blades of this plant, rooted in the bottom, seem to be both 



