252 DESCRIPTION OF [Polyffdstrica. 



namely, the growth of gemmae on the side of the animal- 

 cules, or their pedicles. Although a system of sensation 

 is not indicated by the presence of eyes, we may presume 

 the existence of them, by their great irritability when 

 approached. 



The genera are distributed as follows : — 



!(■ Body covered with cilii Stentor. 

 Tail absent \ 

 { Body smooth, cilii anterior Trichodina. 

 Tail present Urocentrum. 



/ f Stalk flexible, ( Simple ^.Vorticella. 



,form of stalked! deflection spiral | Branched Carchesium. 

 „ . . ,. ,, bodies similar 1 



Body periodically / 



stalked — often V Stalk inflexible Epistylis. 



branched like a tree ; 



Bodies with I Stalk inflexible Opercularia. 



\ ■ ( Stalk flexible, deflection spiral.... Zoothamnium. 



The following curious particulars relating to metamor- 

 phosis are appended to this family bj' Ehrenberg : — 



" The Vorticella developes, a pedicle divides (casts its 

 exuvia), developes posterior cilii, loosens itself from the 

 pedicle, rambles about, draws in (after shedding a second 

 exuvia) the posterior cilii, sheds them, and firmly attaches 

 itself, in order to put forth another stalk and build a 

 trunk. This cycle of phenomena is repeated again and 

 again, and possesses high physiological interest; it is a 

 returning circle of transformations, a return to an early 

 condition, similar to that of a butterfly, if it suddenly 

 lost its wings and antennae, and again became a caterpillar, 

 in order once more to return to the state of pupa and 

 butterfly, or as an old man becoming a child, in order to 

 run again his course of life anew." 



Genus LXXXVII. Stentor. The trumpet Animal- 

 cules comprehend ciliated tail-less Vorticellina, wlio have 



