280 EVENINGS AT THE MICBOSCOPE. 



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 colunan is widely di- 

 vided 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 When the rotatory front is withdrawn, these 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 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 convoluted threads that are believed to be con- 

 nected with respiration, within the lateral wings. The 

 stomachs are generally full of green and brown food, 

 but they will not imbibe carmine. 



Let us look, however, a moment longer at the sin- 

 gular foot. Between the first and second joints there 

 are two projecting spines ; these differ much in differ- 

 ent individuals as to their length, slenderness, and di- 

 rection ; sometimes being quite short, at others as long 

 as the toes ; generally, they arch downwards, but oc- 

 casionally they stand out straight, or even curve up- 

 wards. In some specimens these spines appear to be 

 processes of the first joint, but in others we can see dis- 

 tinctly that they belong to a little intermediate piece 

 between the first and second ajpparent joints. Between 

 the two toes, on the hinder aspect, projects from the 

 last joint a small spine, which is perhaps the rudiment 



