INFUSORIA. 871 



II. Polypi Tubiferi. — Tentaculated polypi, united in a common fleshy 

 body, destitute of solid internal axis, and covered with tubiform cylinders. 



III. Polypi Vaginati. — Tentaculated polypi, constantly fixed in anor- 

 ganic covering, and forming, in general, compound animals. 



IV. Polypi Denubati. — Tentaculated polypi, not forming a common 

 envelope, fixed either constantly or spontaneously. 



V. Polypi Ciliati. — Polypi destitute of tentacula, but with vibralile 

 ciliae, at or near the mouth. 



The habitations of the polypi, or the common masses formed by their 

 united labors, are more or less calcareous or stony, from the madrepores, of 

 a substance as consistent as shells, to the fibrous or membranous horny 

 envelope of the sponge. Between these extremes are found every variety 

 of consolidation and consistence ; but all are formed by animals approach- 

 ing to one another in their general organization. Polypi are reproduced by 

 ova or a separation of parts, natural or accidental. Their food is chiefly 

 animal, derived, in the case of the smaller species, from the infusory ani- 

 malculae which inhabit the waters. 



CLASS XIV. — INFUSORIA. 



Microscopic animals, gelatinous, transparent, polymorphous, and contractile ; 

 no distinct mouth, nor constant or determinable interior organ ; generation 

 fissiparous or gemmiparous. 



The Infusory Animals, or those animalcules which have been observed in 

 infusions of diflerent plants, or in waters, more or less corrupted, and which are 

 generally so minute as to require the aid of the microscope to discover them, 

 form the last series of beings in the animal scale. The greater portion of 

 these appear to have a gelatinous body, of extreme simplicity ; but syste- 

 matical writers have, also, arranged in this class, many animals much more 

 complicated in appearance, and which resemble them only in their extreme 

 minuteness. Of animals so minute, the organization is but imperfectly 

 known. Destitute of a distinct mouth, and internal organ of digestion, they 

 seem to receive nourishment by absorption in all parts of their body. They 

 are, however, capable of contraction and voluntary motion, and their repro- 

 duction is effected by a separation of parts. Lewenhoeck and MuUer first 

 introduced these animals to the notice of naturalists, under the name of 

 Infusoria. In Lamarck's system, they compose the first class of his Inver- 

 tebral Animals ; Dumeril arranges them as the fourth family of his Zoophy- 

 tes ; and Cuvier makes them the fifth class of Zoophytes, or those animals 



