6l8 NEW YORK STATE MUSEUM 



the " neck", or " snout", of the adult. Tliere are here two.separate 

 tubes, one of which conducts water to, and the other from the body 

 within the shell. These organs are long and fleshy in the adult, 

 and reach from the clam's body in the mud up to the water above. 

 In the young- they are relatively small and very delicate. 



The other projection is the so-called " foot " (f), the organ of 

 locomotion. It is here relatively much larger than in the adult, and 

 by its peculiar thrusting and retracting movements, the creature 

 creeps on the surface of foreign bodies, or digs into the sand. 



One of the most interesting features of the life history of M y a 

 is the fact that from a special gland near the base of this foot, a long, 

 nearly transparent thread, the byssus (b), is produced, which is 

 attached to such bodies as stones or pebbles or to floating objects 

 in the water. It acts as an anchor thread, and undoubtedly is devel- 

 oped that the light, minute body of the very small clam may not be 

 floated about by water currents. It completely disappears before the 

 adult condition is reached, and is developed very soon after the little 

 clam ceases swimming. 



These small clams are restless, and apparently always desire to 

 creep about. Though the threads are many times the length of 

 the body, they allow of little movement. From time to time the 

 thread is cast off, for, once attached at its ends to sand grains (s. g. 

 in the figure) or other bodies, it can not be loosed. The clam then 

 slowly creeps about by means of its foot, but soon spins a new 

 thread, at the same time attaching it by its free ends. This may be 

 repeated many times, the clam never remaining for any length of 

 time unattached. 



Very early the young clam manifests the digging instinct. Being 

 a helpless creature, and subject to attack by enemies (notably small 

 starfish), it is necessary that it should cover itself in the bottom as 

 soon as possible. When but little more than a millimeter in length, 

 the creature thrusts its tiny foot down between the sand grains in a 

 tireless effort to obtain a lodgment. This can not be accomplished, 

 however, for the light body is still not much larger than the sand 

 grains which it attempts to displace. When a length of two or 

 three millimeters is reached, the body is sometimes partially or per- 



