lOS 



PROTOZOA 



and is covered with a cuticle, wliicli in Aciin-lj is produced into a cup-like lorica. 

 There is no mouth, but in its place tentacles, very tine tuLies with contractile 

 walls which begin in the protoplasm and protrude through the cuticle (tig. 15S, 

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

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

 rarelv lacking, lies near the compact niacronucleus; niicronuclei are generally 

 present. The ciliated young (fig. 15S, 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 modihcation of the other, part of the 



Fig. 15S. — Suctoria (after various writers'). .4, Pendrosoma: B, Rhynchcia; 

 C, Ophryodciidron; D, Tokoplirya; E, ciliated young of Splnvroplirya: 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 

 Sphcrrophrya, parasitic in Infusoria. Acincta and Podophrya gcmmipara (fig. 

 20) are marine. 



Summary of Important Facts. 



1. The rrotozoa are unicellular organisms without true organs or 

 true tissues. 



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

 directly by its suljstance, locomotion and the taking of food bv means of 

 protoplasmic processes (pscudopociia) or by appendages (cilia and 

 llagclla). 



,V E.xcretion takes f)lace by sjiecial accumulations of lluid, the con- 

 tractile vacuoles. 



4. Reproduction is by liudding or liy llssion. At intervals there is a 

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

 (plasmogamy). Tcrtili/ation may be accomplished bv a permanent 

 fusion (copnilation) or atraiisitor}' union (conjugation) ; it mav be isogamic, 

 anisogainic or autogamic. 



5. Protozoa are a(|uatic, a few living in moist earth; the-\' can onlv exist 

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



6. Since encysted Protozoa are easily carried bv the wiiul, the occur- 



