FIRST BOOK OF ZOOLOGY. 



illustration of the uses of the siphon. In this particular 

 species, the siphon is much longer than the canal, and, when 

 the snail is crawling, the siphon is bent upward. As the 



FIG. 28. A SEA SNAIL SEEN FEOM BELOW. e, Eye; m, Mouth; , Siphon. 



habit of this species is to crawl along partly buried in the 

 mud, the siphon, projecting above the level of the mud, 

 conducts the pure sea- water to the gills of the snail below. 

 Fig. 29 illustrates the appearance of this snail : 



ABC 



FIG. 29. A, the Snail crawling upon the Surface of the Mud ; , the same slightly buried ; (7, 

 the same nearly buried ; the Siphon, , is seen curved upward. 



