520 DEscEiPTiON OF [Polt/cfostrica. 



investigations is attached to the account of each genus to which 

 they refer. 



The genera are distributed as follows : — 



f f Body covered with cilia Stentor. 



I Tail absent ! 



Body without stalk <( ( Body smooth, cilia anterior Trichodina. 



I 



I. Tail present Uroeentrum. 



Body periodically 



bfcilked— often 

 branched like a tree 



f stalk flexible, ( ^^P^^ Vorticella. 

 form of stalked J deflection spiral i -D-o^^vn;! r^ .,„>,„„;„,« 

 bodies similar ^ ^ Branched Carchesmm. 



Stalk inflexible Epistylis. 



Bodies with ( St=*^^ inflexible Opercularia. 



different forms \ gtalk flexible, deflection spiral Zoothamnium. 



The following curious particulars relating to metamorphosis are 

 appended to this family by Ehrenberg : — 



" The Vorticella developes a pedicle ; divides (casts its exuvia) ; 

 developes posterior cilia ; loosens itself from the pedicle, rambles about; 

 draws in (after shedding a second exuvia) the posterior cilia, 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 to that of an old man becoming a child, in order 

 to run again his course of life anew." 



Dujardin describes the Vorticellina under two phases of existence, 

 in the first of which, they are attached by a contractile pedicle, and 

 furnished with a wreath of cilia, interrupted at one point by the 

 mouth ; whilst, in the second stage, they for the most part become 

 detached from their stalk, and swim freely about, whilst the anterior 

 wreath of cilia disappears. At this stage some undulating filaments 

 are developed, from the posterior extremity, as locomotive organs. 

 In the first stage, again, the shape of the body is more or less conical, 

 in the second, more elongated or cylindrical. The metamorphoses 

 of Vorticella during their development, as likewise those oi Epistylis, 

 have been elaborately investigated by Dr. Stein, of BerUn, whilst 

 those of Zoothamnium, have been as ably illustrated by our coxmtry- 



