AC1NETARIA. 825 



with an efferent duct. Reproduction takes place rarely by binary fission or 

 external gemmation, usually by internal. Carnivorous, -feeding on other 

 Protozoa. Freshwater and marine. 



The genus Sphaerophrya is free, and typically parasitic in various 

 Infusoria. It may assume a complete or partial coat of cilia when wander- 

 ing from one host to another. It has been observed that Podophrya liber a, 

 P.fixa, Acineta mystacina, and Dendrocometes, may retract their tentacles, 

 or arms in the case of the last-named, become ciliate and wander away ; 

 and the first-named has been seen to attach itself again. Possibly the 

 phenomenon is not uncommon. The majority of the class are fixed, not 

 infrequently to some animal, and are either sessile or stalked. Trichophrya 

 spreads itself along the surface to which it is attached ; and Dendrosoma 

 forms branching colonies, either erect on a narrow base, or springing from 

 a creeping and anastomosing stolon. 



The surface of the body is very rarely naked (Sphaerophrya, Podo- 

 phrya fixa, Podophrya sp. ?). It is provided with a soft, pliable, and distinct 

 cuticle, or with a firm resistent lorica, e. g. in Acineta, but it is extremely 

 probable that all loricate genera have the parts of the body not protected 

 by the lorica covered with a soft cuticle, the part protected being naked. 

 The soft cuticle perishes soon after the death of the Acinetarian ; when 

 fission takes place it divides with the rest of the body; in external 

 gemmation it is continuous over the buds, and when they separate from 

 the parent organism it separates with them. The lorica varies much in 

 shape ; it may be a shallow plate as in Dendrocometes, a stellate capsule 

 (Acineta stellatd}, or it is a more or less complete cup inclosing the body of 

 the organism to a greater or less extent. Its aperture may take the form 

 of a slit, simple or toothed, of a circular or elliptical figure ; or it may be 

 double. It does not seem certain whether or no the cuticle covering the 

 exposed surface is continuous with its edge. In substance it is firm ; in 

 Acineta gelatinosa, however, soft and gelatinous ; similarly Podophrya 

 limbata has generally a gelatinous investment. If a loricate Acinetarian 

 dwindles in size from any cause, e. g. repeated gemmation, it secretes a 

 septum or additional floor to the lorica on which its body rests. Of such 

 septa there may be more than one. The stalk or peduncle when present 

 is seldom a simple continuation of the cuticle (Fraipont), but has generally 

 a firm tubular wall, sometimes striated both transversely and lengthwise, 

 with clear contents. It is in this case a secreted structure, and when a 

 lorica is also present it is continuous with it. 



The body of an Acinetarian is often changeable in shape, especially in 

 Ophryodendron variabile. The protoplasm has generally an external clear 

 thin layer (ectosarc) : the rest is more or less granular, and pigmented, 

 when well fed. The pigment may be green, yellow, reddish, brown, and it 

 appears to be a useless product of nutrition. When Dendrocometes assumes 



