242 EVENINGS AT THE MICROSCOPE. 



permanent joints with swollen condyles, or rounded heads, 

 resembling those of the antennae of a beetle. Hence the 

 Skeleton has great freedom and precision of motion ; using 

 the tips of the long toes as a fixed point, it throws its 

 body hither and thither to a great distance, with remark- 

 able agility. These joints admit of forward and lateral 

 flexure, but you never see the body brought backward 

 beyond a perpendicular position, the swelling of the ter- 

 minal portion of each articulation precluding further mo- 

 tion in that direction ; 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 Artictjlata, 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 When the rotatory front is withdrawn, these 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 



