CLAMS, OYSTERS, AXD JIUSSELS 



117 



as Limax (Fig. 64). It is dark in color, with two large 

 tentacles on its head, and if looked at closely, will be found 

 to carry a dark, fleshy cape, the rnantle, just V)ack of the 

 head. Some slugs leave a white, shining streak wherever 

 they go, ottdng to the fact that they give out a mucus which 

 hardens in the air. This is done to make a soft silky path 

 over sand and ashes or other harsh substances that would 

 irritate the body. They may be traced long distances and up 



Fig. or. —Slug iLiiiia.v) : o, oper 



to tlie luii^j; ; f, mantle. 



trees, by this shining streak. When ready to descend from 

 the trees, some species spin out a thread of the mucus, like 

 a spider, and drop down by means of it, instead of retracing 

 their path. They often occur in such numl^ers as to be 

 injurious to garden vegetables. 



Sea slugs. — There is a group of marine mollusks, known 

 as the nudibranchs, that have no shells in the adult stage, 

 hence are often called sea slugs or naked mollusks. The 

 gills of these molhrsks are usually arranged in tufts that 

 project from the sides or l^ack of the animal. The sea slugs 

 are of various and striking colors, and vary greatly in shape 



