630 FAMILY: CEECOMONADID.E 



that in all these instances they had developed from cysts of free-living 

 forms. 



Cercomonas longicauda Dujardin, 1841. — The commonest form to 

 appear in old faeces is probably C. longicauda, which was described by 

 Dujardin (1841). It was seen by Klebs (1892), who referred to it as 

 DunorjjJia longicauda. The writer (1910) met with it in stale faeces, and 

 maintained it in culture in hay infusion, and also on agar plates. The 

 flagellate has a more or less pear-shaped body, which varies in length from 

 2 or 3 microns to as much as 18 microns. The shape of the body, which 

 is metabolic, changes very much according to the kind of medium in 

 which the flagellate is living. In surface films it becomes definitely 

 amoeboid. There is no cytostome, and food is ingested in an amoeboid 

 manner. A contractile vacuole has not been seen. Near the anterior 

 region of the body is a nucleus consisting of a nuclear membrane and 

 central karyosome. The membrane is drawn out into a cone-like pro- 

 longation, and at the apex of the cone there commences a rhizoplast formed 

 of two closely applied axonemes, which passes to the anterior end of the 

 body. One axoneme enters a forwardly directed flagellum, which may 

 be two or three times the length of the body. The other passes backwards 

 over the surface of the body to the tapering posterior extremity, where it 

 enters a tail flagellum. At the tip of the nuclear cone, from which the 

 axonemes arise, there is a granule which represents two minute blepharo- 

 plasts. 



Reproduction is by longitudinal division (Fig 259). The first indica- 

 tion of this process is the formation of two new flagella from the granules 

 at the tip of the nuclear cone, while the karyosome takes the form of a 

 band. The granules now divide into two pairs, each of which gives origin 

 to two flagella. The daughter granules move apart, and the nuclear 

 membrane becomes spindle-shaped, while the band of chromatin is 

 arranged as a plate at the equator of the spindle. The plate is made up of 

 a number of chromosomes. By their division two plates are formed, and 

 these pass to opposite poles of the nucleus, which now stretches right 

 across the body of the flagellate, and has a pair of blepharoplasts at each 

 end. The nucleus is finally divided at its centre, and this is followed by 

 division of the flagellate. 



The flagellate becomes encysted in spherical cysts, which are 6 or 7 

 microns in diameter. There is a central nucleus with large karyosome, 

 while the cytoplasm is often filled with refringent granules which stain 

 black with iron haematoxylin. The cysts can be dried, and will give rise 

 to cultures again if placed in suitable medium. 



Woodcock (1916) isolated C. longicauda from the faeces of sheep and 

 goats. He observed the process of syngamy (Fig. 41). Two organisms 



