196 COMPARATIVE ANATOMY 



A frog or toad is killed and its large intestine removed. The 

 contents of the intestine should then be carefully pressed out 

 into a small and perfectly clean glass dish, diluted with a small 

 quantity of a freshly made solution consisting of 20 c.c. egg 

 albumen, i gr. common salt and 200 cc. distilled water, and 

 at once covered with a glass plate. The intestine should 

 not be cut open, and care must be taken to exclude blood or 

 intestinal epithelium from the culture, for if these are present 

 bacterial putrefaction will be set up, which is inimical to the 

 development of Copromonas. After some four or five days 

 the diluted faeces will be found to be swarming with flagellate 

 monads having the structure represented in fig. 42, A. The 

 body of Copromonas is oval or pear-shaped, varying in length 

 from 7*5 to 20 /*, and in breadth from 7 to 8 /*. The whole 

 body is invested by a thin but rigid pellicle except at the 

 narrower or anterior end, where there is a depression con- 

 stituting a cell-mouth or cytostome, leading into a tube, the so- 

 called cytopharynx, which extends backwards with a slightly 

 spiral course and ends in the soft internal protoplasm some- 

 where about the middle of the body. Projecting from the 

 cytostome is a single flagellum or tractellum, whose length is 

 usually somewhat greater than that of the body. In well- 

 stained preparations the basal end of the flagellum is seen to 

 run for a short distance along the wall of the cytopharynx 

 and to take its origin from a distinct basal granule. Under 

 ordinary conditions Copromonas progresses forward with a slow 

 even movement due to the beckoning action of the anterior 

 part of the flagellum, but does not exhibit any euglenoid 

 movements. The pellicle is rigid and non-contractile, and as 

 long as the animal is in a healthy condition the contours of 

 its body remain constant. When stimulated the whole of the 

 flageHum is thrown into vibrations, and the animalcule is able 

 to turn in its course by bending movements of this organ. 



As in Euglena the base or root of the flagellum is in close 

 relation to a relatively large vacuolar space, which is not a 

 contractile vacuole but a reservoir. The contractile vacuole 

 is single or rarely double, minute, rhythmically contractile, and 

 situated at the side of the reservoir farthest from the flagellum. 

 It discharges its contents, at intervals of about half-a-minute, 

 into the reservoir, and the latter would appear to slowly void 

 its contents into the cytostome. 



