408 EVENINGS AT THE MICBOSCOPE. 



flexible but inanimate threads, had any connexion with the 

 sprightly vases which we have been examining ? Yet it is 

 the same animalcule, in what we may, with a certain 

 liberty of phrase, call its chrysalis condition ! 



The history of the Vorticella, as it has been elaborately 

 worked out by Dr. Stein, exhibits phenomena analogous to 

 those marvellous changes which we lately considered under 

 the appellation of the Alternation of Generations. Large 

 individuals withdraw their circle of cilia, close up the 

 mouth, and become globular, and then secrete from their 

 whole surface a gummy substance, which hardens into a 

 spherical transparent shell called a cyst, inclosing the 

 Vorticella in its cavity. Within this cyst is seen the hand- 

 shaped nucleus, unchanged, and what was the contractile 

 bladder, which, however, no longer contracts. 



By-and-by this torpid Vorticella enlarges itself irregularly, 

 pushing out its substance in tufts of threads, and frequently 

 protruding from one side a larger mass, which becomes an 

 adhering stalk. Thus it has become an Acineta, such as 

 we now behold. 



From this condition two widely different results may 

 proceed. In the one case, the encysted Vorticella sepa- 

 rates itself from the walls of the Acineta, contracts into an 

 oval body, furnished at one end with a circle of vibratory 

 cilia, by whose movements it rotates vigorously in its 

 prison, while the more obtuse end is perforated by a mouth 

 leading into an internal cavity. In the interior of this 

 active oval body there are seen the band-like nucleus, and 

 a cavity which has again begun to contract and to expand 

 at regular intervals. It is, in fact, in every respect like a 

 Vorticella vase, which has just freed itself from its stalk. 

 Presently, the perpetual ciliary action so far thins away the 

 walls of the Acineta that they burst at some point or other, 

 and the little Vorticella breaks out of prison, and com- 

 mences life afresh. The Acineta, meanwhile, soon heals 

 its wound, and after a while develops a new nucleus, which 



