252 DESCRIPTION OF [Polygastrica. 



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 : 



/ f Body covered with cilii Stentor. 



Tail absent J 



Body without stalk J ( Body smooth, cilii anterior Trichodina. 



\Tail present Urocentrum. 



Stalk flexible, ( Sim P le ^orticella. 



xible, ( 

 spiral j 



form of stalked deflection spiral j Branched Carchesium. 

 Body periodically ! bodies similar j 



stalked often x \ Stalk inflexible Epistylis. 



branched like a tree j 



Bodies with | Stalk inflexible, Opercularia. 



(different forms j gtajk flexible> deflection spiral.... Zoothamnium. 



The following curious particulars relating to metamor- 

 phosis are appended to this family by 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, who have 



