140 MOLLUSCA 



Mead and Barnes: Observations on the Soft-shell Clam. Rhode Island 



Com. Inland Fish., 20 to 24, 1900 to 1904. 

 Yonge: Studies on the Comparative Physiology of Digestion. I. The 



Mechanism of Feeding, Digestion, and Assimilation of the Lamelli- 



branch Mya. Brit. Jour. Exp. Biol., 1, 1923. 



ENSIS DIRECTUS (Razor-shell Clam) 



This species is another representative of the order Eula- 

 mellibranchia and is introduced because of its adaptation for 

 a burrowing habit, and because of the great ease with which 

 its nervous system can be studied. Individuals are not un- 

 common on mud or sand flats from which the water flows 

 at low tide. They may sometimes be seen protruding above 

 the surface of the mud, but are hard to approach because 

 of their great sensitiveness. Upon being disturbed they 

 quickly disappear beneath the surface of the mud. These 

 animals are sometimes used for food. They are frequently 

 collected in Japan by placing a little common salt in the 

 opening of the burrows. Within a few seconds an animal so 

 treated energetically backs out of its burrow. 



1. Notice the shape of the shell, the way it gapes at both 

 ends, and the way the lobes of the mantle are fused. 



2. With a pencil point or seeker stroke the tentacles 

 around the siphon openings, while the animal is being held 

 anterior end downward. This will cause it to perform the 

 burrowing movements. Study the movements carefully and 

 see what the effects would be were they performed in mud. 

 Thrust the anterior end of the shell in mud and watch the 

 result of the movements. 



3. Water is ejected by the sides of the foot to aid in bur- 

 rowing or to enable the animal to swim, but observations on 

 its method of ejecting it are not easily made, and are sure to 

 take much time. Notice the way the anterior margins of the 

 lobes of the mantle scrape mud from the foot when the foot 

 is being withdrawn. 



4. With a scalpel separate the united margins of the 

 mantle throughout their length. Slowly pry the valves apart, 

 lift up the free end of the foot and pull it posteriorly. 



