INFUSORIA. IO3 



The Paramecians are propagated by spontaneous division, as 

 already described. They abound, as we have said, in semi-stagnant 

 water, or in pure water which is occupied by aquatic plants, some- 

 times in such prodigious quantities that they become troublesome. 

 They may occur also in flower vases where the water is not frequently 

 renewed. 



The species of this genus have an oblong compressed body, with 

 an oblique longitudinal fold, directed towards the mouth, which is 

 lateral. They are sufficiently large to be observed with a common 

 lens, or eye-glass. Paramecium aurelia is common in ditches, or 

 ponds, and moats, with aquatic plants. 



Humboldt's assertion is fully verified in the case of the Infusorian 

 under consideration, which is often found with its parasites (vide 

 Fig 28). These are small creatures, cylindrical in form, and provided 

 with suckers. Swimming vigorously in the water, they devote them- 

 selves to chasing the Paramecium. When they have overtaken the 

 fugitive, they throw themselves upon it, and establish themselves 

 there. They soon multiply in the interior of its body, and their 

 progeny suck and devour the unfortunate animalcule, which thus 

 serves them at once for dwelling-house and larder. 



Another of the parasites which prey upon the Paramecium, in 

 place of pursuing it, remains perfectly quiet until one of these 

 approach, when it throws itself upon its victim, and is carried along 

 with it. It buries itself in the body of the Paramecium, and, in a 

 short time, multiplies to such a degree, that sometimes fifty of them 

 are found on a single individual. 



The species of the genus Nassula have the body entirely covered 

 with cilia ; they are ovoid or oblong in form, contractile, their mouth 

 is placed laterally, and provided with a circlet of teeth in the form of 

 a wheel (nassa), this circlet dilating and contracting according to the 

 size of the prey which it would swallow. They will either advance to 

 seize the prey, which the movement of the vibratile cilia have failed 

 to draw within the vortex of their mouth, or, as in the case of the 

 Paramecium, they are sometimes obliged to seek for their prey. 

 These curious Infusoria live in fresh water, feeding on the debris of 

 aquatic plants, from which they draw their chief nourishment. Their 

 colour is white or greenish, sometimes a brownish green, variegated 

 with violet vesicles. 



The genus Bursaria contains animals with an oval or oblong con- 

 tractile body, provided also with vibratile cilia on the surface, having 

 also a large mouth, surrounded with cilia, forming a sort of micro- 

 scopic moustache, spirally arranged. 



