408 EVENINGS AT THE MICROSCOPE. 



nexion with the sprightly vases which we have been 

 examining 1 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 con- 

 tractile bladder, which, however, no longer contracts. 



By-and-by this torpid Vorticella enlarges itself irregu- 

 larly, 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 

 iproceed. 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 Vorti- 

 cella breaks out of prison, and begins life afresh. The 

 Acineta, meanwhile, soon heals its wound, and after 



