THE INFUSORIA 411 



in irregular rows or unevenly scattered. The HYPOTRICHA are usually 

 found creeping on the surface of animals, plants, the scum of putrefac- 

 tions, or the surface film of water. The progression is effected entirely 

 by the cilia or cirri on the ventral surface of the body, which are used 

 like the legs of higher animals. The most modified form is Stichospira 

 (Fig. 71), which is elongated in shape and uses its ventral cirri to 

 crawl up and down a short mucilaginous tube which it constructs on 

 the epidermis of plants. 



The HYPOTRICHA are nearly all small (*3 to '4 mm.) or very small 

 (Q3-'01 mm.) in size, and they are usually very active in their move- 

 ments. The meganucleus sometimes exhibits a remarkable fragmentation 

 during the intervals between the acts of fission as described on p. 372 

 (Figs. 16 and 17). A majority of the genera have been described by 

 authors as possessing either two nuclei or a single two-jointed nucleus. 

 It is probable that this double- or twin-nucleus condition is one phase, 

 characterised by its considerable duration, in the process of nuclear 

 fragmentation. Stylonychia and Euplotes each possess one minute micro- 

 nucleus, but in most of the genera very little is known about the 

 micronuclei. 



The order HYPOTRICHA is divided into the following families : 

 Family PERITROMINA, Stein. Peritromus, Stein. This is the simplest 

 form of the HYPOTRICHA, the ventral ciliation being uniform and dense 

 and without any differentiation of stouter cilia or cirri. 0*1. Marine. 



Family OXYTRICHINA, Stein. Trichogaster, Sterki. 0'23. Fresh- 

 water. Urostyla, Ehrb. Elongated in form. Ventral cirri arranged in five 

 or more longitudinal rows. Enlarged cirri in the frontal region and in a 

 transverse row near the posterior extremity. 0*3. Marine and fresh- 

 water. Kerona, Ehrb. Kidney-shaped. Six or seven oblique rows of 

 small cirri on the ventral side. 0-15. Found creeping on the ectoderm 

 of Hydra. Epiclintes, Stein. The number of rows of ventral cirri is 

 reduced to five or six, but there are no special frontal or caudal cirri. 

 0'3. Marine. Stichotricha, Perty. The anterior extremity is prolonged 

 into an extremely flexible proboscis, on which the adoral zone is extended. 

 Either free or attached by gelatinous tubes, which sometimes form den- 

 dritic colonies. O'l. Marine and freshwater. Stichospira, Sterki. On 

 freshwater plants (Fig. 71). Strongylidium, Sterki. Freshwater. Holo- 

 sticha, Entz. Two rows of marginal cirri, between which are two or three 

 rows of cirri without special differentiation of frontal cirri. A tranverse 

 row of caudal cirri. 0*4. Marine. Amphisia, Sterki. With differen- 

 tiated frontal cirri. Marine and freshwater. Uroleptus, Ehrb. Three 

 well -developed frontal cirri. Sometimes rose or violet in colour. 0'5. 

 Marine and freshwater. Sparotricha, Entz. Similar to Spirotricha, but 

 the adoral zone does not extend beyond the middle of the proboscis. O'l. 

 Salt marshes in Hungary. 



Family PLEUROTRICHINA, Biitschli. In this family the frontal cirri 

 are well developed and usually eight in number. There are also specialised 

 abdominal and caudal cirri. Onychodromus, Stein. Three or four ab- 

 dominal cirri. 0'35. Freshwater. Pleurotricha, Stein. Five strongly- 

 developed abdominal cirri and a row of five transverse caudal cirri. 0*4. 



