MUSCULAR POWER. 25 



body, in others only forming a shield. This 

 shell is called a Zorica, and the term loricated 

 is used to point out the species having a shell. 

 None are supposed to have internal bones, but 

 their muscles must be of the most complicated 

 construction, to enable them to move easily and 

 rapidly, which many of them do in an astonish- 

 ing degree. One species (Vorticetta convattarid) 

 is attached to leaves and stalks, by a transparent 

 thread of some length : this it has the power of 

 suddenly contracting when danger threatens, so 

 that the body is instantaneously removed to a 

 distance. The muscles in this thread-like stalk 

 are so contrived, that it assumes on these occa- 

 sions a corkscrew or spiral form, and this action 

 brings the body close to the leaf on which it is 



D 



