WHEEL-BEARERS 277 



tion; just as the joints of our knees and elbows permit 

 bending in one direction but not in the other. 



This is another indication that these divisions are true 

 joints; and I direct your attention to the point, because 

 the fact helps to indicate that this class of animals has its 

 proper affinities with the ARTICULATA, which has been 

 denied by most naturalists. 



The form is curious. Elevated at the summit of a long 

 foot, consisting of three joints, which surmount two un- 

 usually lengthened and slender toes, is a vase-shaped 

 lorica, which is three-sided. Its surface is covered all 

 over with minute points, very closely set, so that it re- 

 sembles shagreen; besides which it forms numerous sharp 

 ridges, which run across transversely. The two sides run 

 off into thin lateral wings, which come to a sharp edge; 

 the back angle also forms a ridge, but less sharp and 

 thin. In front, the shell, or lorica, is as it were cut off 

 abruptly, like the rim of a goblet, but out of this rises 

 a second column, connected with the rim by an elastic 

 membrane, which allows some freedom of motion. This 

 column is widely divided in front and behind, and rises 

 to a point on each side. When the rotatory front is with- 

 drawn, these points approach and meet, closing the orifice; 

 but when the head is protruded they are widely separated. 



Internally, we see the usual viscera contained in so 

 narrow a cavity that we are ready to suppose the walls 

 of the lorica unusually thick; this is, however, an optical 

 illusion, dependent on its dilatation into those angular 

 wings already noticed. The cavity penetrates into them; 

 for in one of these specimens I see those curious convo- 

 luted threads that are believed to be connected with res- 

 piration, within the lateral wings. The stomachs are gen- 



