232 THE GILLS AND SPEAES. 



tube alone (the animal liaving deserted it) was lield 

 lip full of water, the fluid ran out rapidlj at the same 

 aperture. The animal, also, which voluntarily crawled 

 out of its habitation, displays no such reversion of 

 the tail as is described by Dr. Williams. This organ 

 is a little leaf-shaped body, formed by the union of 

 several short segments, and slightly bent downward, 

 but not reverted. 



The quitting of its tenement by the Worm enabled 

 me to see and admire some other points in its struc- 

 ture, and their subservience to its economy. On each 

 side of the neck, just below the edge of the flat, cork- 

 like head, are seen two little scarlet gills, resembling 

 in structure those of fishes. Each consists of a free 

 leaflet, formed of numerous thin plates set face to 

 face : in health these little pointed gills are thrown 

 about with agility in various directions, and their 

 points alternately coiled up and unfolded. Behind 

 these, along each side of the body, are placed promi- 

 nent, fleshy warts, to the number of fifteen pairs ; 

 each of which consists of two j)ortions, the hinder 

 part being dilated into a soft transverse mop, and the 

 fore part perforated to give exit to a brush of fine 

 spears of elaborate construction. They are about 

 twelve in each bundle, each formed of a long and 

 slender, highly elastic, glassy shaft, terminated by a 

 bent blade, the edge of which is of the most delicate 

 thinness, and the point of which is drawn out to gTeat 

 length and tenuity. Some of the blades appear to be 

 simple and knife-like, but others have the edge cut 

 with oblique slits, parallel to each other, and pointing 

 from the base. They do not form saw-teeth, but are 



