THE OILIATE INFUSORIA. 39 



away, both assuming the common form of the animalcule 

 when free-swimming, and differing from the original indi- 

 vidual only in being of smaller size." 



The most complicated as well as most interesting form of 

 all the Infusoria is the bell-animalcule, Vorticella. It is 

 very common in pools, forming patches like white mould on 

 the leaves and stems of submerged plants. It may, like 

 Stentor, be observed under low powers of the microscope. 

 Their motions, as they suddenly contract and then shoot 

 out their bell, mounted on a long stalk, are very interesting. 

 The throat (oesophagus) is quite distinct, while the nucleus 

 is the most conspicuous organ of the body. The digestive 

 cavity is a large hollow in the protoplasm forming the body- 

 mass, in which the whole mass of food revolves in a deter- 

 minate channel. Closely allied to Vorticella is JSpistylis 

 (Figs. 27 and 28). 



While most ciliate Infusoria, so far as known, multiply 

 by self-division, in Vaginicola the process is more like true 

 gemmation or budding, and is accompanied by a process of 

 encysting, resulting in the production of a free-swimming 

 ciliated embryo, the adult Vaginicola being attached. The 

 FoWiceZto also becomes encysted, and the nucleus subdivides 

 until the body becomes filled with monad-like germs, the 

 result of the simultaneous breaking up of the nucleus. The 

 VorticellcB, then, pass through a flagellate or monad stage, 

 from which they pass into the Vorticella condition, when 

 they multiply by self-division and by budding, the last 

 generation becoming encysted. 



Conjugation is a common occurrence in ciliate Infusoria, 

 and results in the breaking tip of the nucleus of each indi- 

 vidual into a number of fragments, and the appearance in 

 each of the individuals of the nucleus and nucleolus (either 

 single or multiple) which characterize the species.* 



* Balbiani believes that the ciliate Infusoria have eggs which are 

 fertilized by spermatic particles. More lecently, however, Engelmann, 

 Blitschli, and Hertwig have denied that conjugation is of a truly sexual 

 character, and that the striated nucleoli of certain individual Infusoria 

 are spermatozoa. " Nevertheless," remarks Huxley (Anatomy of In- 



