COPKOZOIC EUGLENOIDIDA 283 



that the form which was named Copromonas subtilis by Dobell is identical 

 with Scytomonas pusilla Stein, 1878. 



Copromonas subtilis was first described by Dobell (19086) from the 

 faeces of frogs and toads. Dobell and O'Connor (1921) report its occurrence 

 once in human fseces, not as a parasite in the freshly passed stool, but as a 

 coprozoic organism which had evidently developed from cysts after the 

 stool had been passed. The writer has seen this flagellate in cultures 

 of pig's fseces. It is an elongate organism with an average length of 

 15 microns (Fig. 133). Longer forms up to 20 microns and smaller ones 

 of 4-5 microns also occur. The body is covered with a thick, rigid pellicle, 

 so that there is little change of shape. The anterior end is somewhat 

 pointed, and there is here a cytostome leading to an oesophagus which 

 extends through half the length of the body, the posterior end of which 

 is rounded. There is a single flagellum, which arises from a blepharoplast 

 situated in the wall of the oesophagus near the nucleus. During forward 

 progression the tapering flagellum projects as a rigid filament, the move- 

 ments being confined to the distal third or half. According to Dobell, near 

 the blepharoplast is a clear vesicle, the reservoir, into which the contents 

 of a minute contractile vacuole are periodically discharged. The nucleus 

 is centrally placed, and consists of a spherical membrane and a large 

 central karyosome. Multiplication is by longitudinal division from before 

 backwards, after division of the nucleus and blepharoplast. The flagellum 

 is discarded, and after division of the blepharoplast two new flagella are 

 developed as outgrowths from the two daughter blepharoplasts, which, 

 during division, remain connected by a long fibre which lies transversely 

 across the body and parallel to the spindle of the dividing nucleus. Syn- 

 gamy occurs, as first described by Dobell (19086). Two flagellates unite 

 by their anterior ends, the union extending backwards till their two bodies 

 are completely fused (Fig. 48). Each nucleus is described as undergoing 

 a reduction of its chromatin, after which union takes place. During the 

 conjugation one flagellum is withdrawn, so that the zygote has a single 

 flagellum, by means of which it moves about actively. The zygote may 

 commence dividing after leading a free existence for some time, or it may 

 encyst. Encystment may also occur without conjugation. The cysts 

 are ovoid or spherical structures with thin walls and clear contents. They 

 measure 7 to 8 microns in length. Berliner (1909) gave the name Copro- 

 monas major to a form which he cultivated on agar plates from the faeces 

 of lizards. Like the form cultivated from goat's fseces by Woodcock 

 (1916), which he named Copromonas ruminantium, it is slightly larger than 

 C. subtilis. Both these may be merely races of the smaller flagellate. 

 Berliner stated that the flagellates were sometimes present in the free- 

 swimming stage in the intestine of lizards. 



