THE INFUSORIA 405 



ORDER Heterotricha, Stein. 



This order includes those Ciliata in which there is a special adoral 

 zone, armed with specialised long or thick cilia, supported by a delicate 

 protoplasmic ridge or membranella, and usually spiral in form. 



The Order is divided into two Sub-orders : 



Sub-order POLYTHICHA. 

 Sub-order OLIGOTRICHA. 



The sub-order POLYTRICHA includes those HETEROTRICHA in which the 

 general surface of the body is covered with rows of short cilia. The 

 longer cilia are usually confined to the adoral zone, but may also occur 

 in the form of a tuft (Metopus) at the posterior end of the body. The 

 form of the body may be spherical (Bursaria), oval (Condylostoma), rod- 

 like (Spirostomum), or trumpet-shaped (Stentor and Folliculina). Most of 

 the genera are permanently free -swimming, but some are occasionally 

 (Stentor) or usually (Folliculina) sedentary in habit. In Bursaria, Balan- 

 tidium, and others the mouth is at the anterior end of the body. In 

 Chonchophthirus and Spirostomum it is near the middle, whilst in Plagio- 

 toma it is situated nearer to the posterior than to the anterior end. 



This sub-order contains some of the largest Ciliata. The elongated 

 Spirostomum may be 3 mm. in length, Bursaria is occasionally 1'5 mm. in 

 diameter, and Stentor and Folliculina 1 mm. in length in the extended 

 condition. Some genera (Stentor, Folliculina) have considerable powers of 

 contracting and extending the body. In Spirostomum the contraction is 

 spiral. Trichocysts have not yet been discovered in any POLYTRICHA. 

 The meganucleus is oval in Nyctotherus, Blepharisma, Balantidium, and 

 others. In Spirostomum it is oval at one time and at others it becomes 

 very elongated and moniliform. In Stentor it is moniliform (Fig. 44). 

 In Playiotoma and Bursaria it is elongated. In Balantidium and others 

 only one micronucleus has been seen ; but in Stentor, Bursaria, Spirosto- 

 mum, etc., there are numerous micronuclei. 



The POLYTRICHA contain the following families : 



Family PLAGIOTOMINA, Clap, and L. Conchophthirus, Stein. The 

 adoral zone represented by a row of long cilia on the anterior border of 

 the peristome. 0'2. Ectoparasitic on the mucus of several fresh- and 

 salt-water Pelecypoda. Also found in the body-cavity of various species 

 of Actiniaria. Plagiotoma, Duj. Slightly contractile. Meganucleus a 

 long twisted band. 0'4. Parasitic in the intestine of earthworms. 

 Nyctotherus, Leidy. This is regarded as a sub-genus of Plagiotoma by 

 Biitschli. It is distinguished from it by its reniform shape and by the 

 sausage-shaped or oval meganucleus. 0'3. Parasitic in the intestines. of 

 Anura and various insects and myriopods. (Fig. 56.) Blepharisma, Perty. 

 Very similar to Plagiotoma, but not parasitic. 0'4. Freshwater. Metopus, 

 Clap, and L. Oval in form, with a well-developed peristome sinistrally 

 twisted. There is frequently a large pigmented spot at the anterior end 

 of the body. 0'3. Marine and freshwater. Spirostomum, Ehrb. The 

 longest of all the Ciliata. It contracts rapidly in a spiral manner. Very 



