170 



GENERAL ZOOLOGY 



the margin of the mantle, the mantle is withdrawn and some- 

 times the valves are closed. The same experiment may be 

 tried on the oyster with similar results, although the oyster 

 has no eyes at all. Invisible sense-organs in that animal 

 respond to the stimulus of light. 



While feeding and breathing, the tentacles of the scallop 

 aid the cilia of the mantle, gills, and palps in conveying food 

 to the mouth. At such times the spores of various seaweeds 

 and the young of certain snails (Crepid'ula, on 

 scallop in foreground, Fig. 87) may find a surface 

 of attachment on one of the valves. These 

 organisms have an advantage over station- 

 ary individuals of the same species, 

 in being attached to a movable 

 support, for, when the scallop 

 swims about, the messmates are 

 carried to new and possibly 

 better stores of food. 



If one were to reason from 

 the general appearance of the 

 scallop which part should go for- 

 ward when the animal swims, it 

 is verv likely that the conclusion 





FIG. 87. Group of Living Scallops. 



