94 



Protozoa. 



winds, together with other dust, and thus they appear quickly 

 wherever it is possible for them to exist. 



1. Of the iminmerable freeli-water Infusoria, the following common forms 

 may be mentioned : Paramxciwm, body oval, covered -witli uniform rows of cilia 

 Stylonychia, oval, with a series of cilia, anteriorly, leading to the mouth, and 



Pig. 52. 



Fig. 53. 



rig. 52. 1 An Infuaorian ^Parcumcecivm). 2 — 4 The same in various stages of 

 division ; in 2 the mouth and contractile vacuole are re-duplicated ; in 3 the macro- and 

 micro- nuclei are much elongated and constricted, in 4 they have divided, cv contractile 

 vacuole, cv' newly-formed vacuole, o mouth, o' newly-formed month, N macro-, n micro- 

 nucleus. — After Biitsohli. 



Pig. 53. Vorticella; lower portion of the stalk not drawn, 

 s stalk. Other letters as in Fig. 52. — After Biitsohli. 



na food particles, 



with strong spiny or hook-like cilia ventrally; Vorticella (Bell-animalcule), 

 a stalked Infusorian furnished with spirally arranged cilia at the anterior end, but 

 otherwise naked ; moxith and anus situated in a common groove, anteriorly : at 

 the opposite end arises a stalk, through which runs a muscular thread. By 

 means of the stalk, which is frequently very long, the animal attaches itseH to 

 various foreign bodies. The Vorticellse may sometimes break free from their 

 stalks, and become free-swimming.* Many form branched colonies. 



2. Many species belonging to the genus Tintinnus, etc., and bearing very 

 beautiful chitinous shells, are sometimes found in great numbers in the 

 open sea. 



3. As an example of parasitic Infusoria, Balantidiwm coli may be mentioned ; 

 it is always present in the large intestine of the Pig, and more rarely in Man. 

 The body is egg-shaped, uniformly covered with ciKa, but with a somewhat 

 stronger series near the mouth. Other Infusoria occur, e.g., in the paunch of 

 Ruminants, and in the large intestine of the Horse. 



* The conjugation of the Vortioellids is interesting. It occurs between a larger 

 sessile individual or maorozoid, and a smaller free-swimming microzoid. The latter 

 attaches itself to the larger one, and conjugation occurs in the ordinary way ; after 

 the exchange of the micronucleus, however, the protoplasm of the microzoid is 

 absorbed into that of the maorozoid, and the empty cuticle of the former drops off. 



