66 THE SCALLOP FISHERY 



from the water. Lying free in the body cavity, they are constantly 

 surrounded by the flowing water, which passes through and around the 

 filamentous bars. When examined under a microscope the gills are 

 found to be covered by small hair-like cilia, lashing in a definite direc- 

 tion. These cilia cause currents of water to pass over and through the 

 gills, while other cilia between the filaments act as minute sieves to 

 strain out the food particles, which are at once cemented together with 

 a mucus and propelled by the ciliary action toward the popularly 

 called " backbone " of the gills, or the dorsal edge. Here they are taken 

 up in a more definite channel and swept with increasing velocity toward 

 the upper end of the gills to the lower edges of the palps. The palps 

 are ridged and furrowed like the gills, and the food is transferred to 

 the mouth by means of these " lips." If an excess of food or foreign 

 matter is caught by the gills, the animal, by a complicated mechanism, 

 as described by Kellogg (3), is able to cast it off. 



The effete matter from the digestive tract is carried out from the 

 shell at the posterior pseudo-siphon. The waste in transverse section 

 has the appearance of a three-leafed clover, Jackson (4), and is of 

 uniform length. When the scallop lies feeding in the aquarium, the 

 feces pass out at regular intervals of about a minute, suggesting a 

 nearly constant need of food. The constant flow of water through the 

 shell shows that the other parts, such as mantle, visceral mass, etc., must 

 likewise be ciliated as well as the gills, in order to force the flow of 

 water in one direction, an entirely different arrangement from the 

 ejection of water by the mantle in swimming. 



SENSORY POWERS. 



The exact reactions of the scallop to light and other external stimuli 

 have never been worked out, and there remains a wide field for investi- 

 gation on these points, especially in regard to the effect of light. The 

 following are a few meager observations which it is hoped may interest 

 some one to take up the study of the sensory powers of the scallop. 



The scallop is sensitive to a sharp tap or sudden jar. When small 

 6-millimeter scallops are attached to the sides of glass dishes, the valves 

 remain open, tentacles extended. A sharp tap on the outside of the jar 

 directly over the animal causes it to retract its tentacles, but after 

 repeated tapping the creature does not seem in the least disturbed, as 

 the tentacles remain extended. All motions outside the glass dish were 

 unnoticed by the scallop. 



At times the adult scallop is quite sensitive; again, the same stimulus 

 does not excite the animal. Evidently it has various moods. Jack- 

 son (4) states that when spinning the byssus the scallop appears undis- 

 turbed by pricks, etc. As cold weather comes on the animal becomes 

 less active and fails to respond with its former alertness. 



The eyesight of the animal has aroused considerable comment. The 



