198 



PROTOZOA 



and is covered with a cuticle, which in Acineta is produced into a cup-like lorica. 

 There is no mouth, but in its place tentacles, very fine tubes with contractile 

 walls which begin in the protoplasm and protrude through the cuticle (fig. 158, 

 F}. The Acinetaria kill other animals, especially infusoria, with their tentacles, 

 and then suck the substance through these tubes. The contractile vacuole, 

 rarely lacking, lies near the compact macronucleus; micronuclei are generally 

 present. The ciliated young (fig. 158, E) are good swimmers. They arise 

 either as buds from the surface of the mother (fig. 20) or as 'embryos' in her 

 interior. This latter condition is only a modification of the other, part of the 



FIG. 158. Suctoria (after various writers). A, Dendrosoma; B, Rhyncheta; 

 C, Ophryodendron; D, Tokophrya; E, ciliated young of Sphcerophrya; F, diagram of 

 capitate and styliform tentacles arising from ectosarc and canals in entosarc. 



outer surface being pushed into the interior to form a brood cavity in which the 

 embryos arise. After swimming for a while the young come to rest, lose the 

 cilia, and develop the tentacles. Some species of Podophrya in fresh water, also 

 Sphcerophrya, parasitic in Infusoria. Acineta and Podophrya gemmipara (fig. 

 20) are marine. 



Summary of Important Facts. 



1. The Protozoa are unicellular organisms without true organs or 

 true tissues. 



2. All vital processes are accomplished by the protoplasm, digestion 

 directly by its substance, locomotion and the taking of food by means of 

 protoplasmic processes (pseudopodia) or by appendages (cilia and 

 flagella). 



3. Excretion takes place by special accumulations of fluid, the con- 

 tractile vacuoles. 



4. Reproduction is by budding or by fission. At intervals there is a 

 true fertilization (caryogamy) sharply distinct from mere fusion of plasma 

 (plasmogamy). Fertilization may be accomplished by a permanent 

 fusion (copulation) or a transitory union (conjugation) ; it may be isogamic, 

 anisogamic or autogamic. 



5. Protozoa are aquatic, a few living in moist earth; they can only exist 



in dry air, surrounded by a capsule (encysted) which prevents desiccation. 



6. Since encysted Protozoa are easily carried by the wind, the occur- 



