136 MANTON COPELAXD. 



objects on the expanded ciliary surface. In this manner it was 

 found that a five-cent piece and good-sized pebbles were readily 

 moved by the beating cilia. Following these preliminary tests, a 

 carrier weighing slightly over half a gram was made by fastening 

 a glass ring on a 22 mm. cover glass. A 2O-gram weight was then 

 set on the ring, and the cover glass placed on the upturned middle 

 portion of the foot, which in turn was supported so that the cilia 

 were at about the level of the surface of the water. When the 

 snail began the righting reaction the beating cilia moved the mucus 

 and carrier with its load toward the posterior end of the foot. 

 One of the animals tested in this way weighed between 8 and 9 

 grams in water and had a pedal ciliated surface with foot expanded 

 of about 54 square cm. Thus between 4 and 5 square cm. of active 

 cilia were able to move not less than 20 grams, whereas during 

 locomotion the task of moving 8 grams was distributed over an 

 area of 50 square cm. The largest specimen of Polinlces duplicata 

 which I was able to obtain weighed only 36 grams in water and its 

 locomotor surface measured about 132 square cm. Although the 

 resistance of the water to be overcome by the moving animal is a 

 factor to be considered in any detailed calculation of the work re- 

 quired of the locomotor apparatus, the results of these tests leave 

 no doubt as to its adequacy. 



Although Polinlces was once observed to move a short distance 

 clinging to the under side of a glass plate with the propodium un- 

 attached to the glass, it is the anterior border of this organ which 

 as a rule holds most tenaciously to the substrate when one attempts 

 to dislodge the snail. Several times I have seen one move up the 

 glass side of an aquarium until it came to the surface of the water, 

 when it turned the propodium downward, or perhaps parallel to the 

 surface, and lifted it from the glass. Soon after relinquishing this 

 anterior hold it slipped to the bottom. Moreover, it is able to 

 cling to the under side of a glass plate by the propodium alone and 

 to advance several centimeters by muscular action. Evidently, 

 therefore, this specialized portion of the foot has considerable 

 power of suction, although adhesion by means of mucus is in all 

 probability the principal mode of attachment for the foot as a 

 whole. When the snail is moving the anterior margin of the pro- 

 podium is in close contact with the substrate and exhibits con- 



