21 



PROTOZOA. 



species. These are the best forms for studying the micronnclei. 

 The species of StylonycMa* (figs. 151, 152) are best known. 



Order V. Suctoria (Acinetaria). 



The Suctoria diiler from other Infusoria in the absence of cilia 

 from the adult and consequently have no means of locomotion. 

 They are fixed to some support either by the base or by a slender 

 stalk. The body is usually spherical and is covered with a cuticle, 

 which in the genus Acineta is produced into a cnp-like lorica. 

 There is no mouth, but in its place tentacles or sucking feet, very 

 fine tubes with contractile walls which begin in the j)rotoplasni and 

 protrude through the cuticle (fig. 153, F). The Acinetaria kill 

 other animals, especially infusoria, with their tentacles, and then 



Fig. 153.— Forms of Suctoria. (After various writers.) A, Detidrosoma : B, Rhiincheta: 

 C, Ophnjodeiidron: D, Tokophryu: E, ciliated young of Sphcerophri/a : F, diagram of 

 structure showing capitate and stylitorm tentacles arising from the ectosarc 

 and corresponding canals in the entosarc. 



suck the substance through these tubes. The contractile vacuole, 

 rarely lacking, lies near the compact macronucleus; micronuclei 

 are generally jiresent. 



In contrast to the immobile adults the young which are ciliated 

 (fig. 15.3, U) after the pattern of ciliates. are good swimmers. 

 They arise either as buds from the surface of the mother or as 

 ' embryos ' in her interior. This latter condition is only a modifi- 

 cation of the other, for parts of the outer surface become pushed 

 into the interior, and there form a brood cavity in which the 

 embryos arise. After swimjning for a while the young come to 

 rest, lose the cilia, and develop the tentacles. 



Some species of Podophri/a are widely distributed in fresh water, also 

 SpJuerophrya, parasitic in Infusoria. The species of Acineta as well as 

 Podophri/a yemmipara (fig. 20) are marine, living ou hydroids aud Poly- 

 zoa. 



