INTESTINAL PROTOZOA 591 



as a free posterior ttagellum. Other structures present are the 

 cytostome, a slight conical depression near the nucleus, a stiff rod 

 running along the base of the undulating membrane, and the 

 axostyle, a clear refractile bar arising near the cytostome, and 

 continued through the body towards the posterior end where it 

 protrudes through the surface as a sharp point (Plate XXIII, i). 

 The cytoplasm is often vacuolated, the vacuoles containing bac- 

 teria. The flagellate is actively motile. The flagella are best 

 seen with dark ground illumination. For diagnosis, it is important 

 to count the three anterior flagella, as only by this character can 

 it be distinguished from two closely allied, though much rarer 

 forms Tetratrichomonas which possesses four anterior flagella, 

 and Pentatrichomonas which has five. 



Keproduction takes place by longitudinal fission. Encystment 

 does not appear to occur, but by a casting off of the flagella an 

 amoeboid cytoplasmic mass is formed, still possessing the undulat- 

 ing membrane at one edge (Plate XXIII, k). It was this form 

 which Castellani probably described as Entamceba undulans of 

 the human intestine. 



Trichomonas is common in rats, mice, fowls and other animals. 

 Hadley * holds that it is the cause of dysenteric affections in 

 turkeys ("blackhead disease") and poultry, in which it causes 

 necrosis of the csecal epithelium and necrotic foci in the liver. 



A very similar, though larger (15-30 p.), form, Trichomonas 

 vaginalis, is common in the vagina. 



Giardia (Lamblia) intestinalis 



This flagellate is fairly common and inhabits the upper part of 

 the small intestine. Infection is often abundant, and is very 

 persistent, and though for the most part unassociated with 

 symptoms, from time to time abdominal uneasiness and attacks 

 of diarrhoea may occur. In the rabbit, the parasite may invade 

 the glands of the small intestine. 



Giardia in shape somewhat resembles the half of a pear split 

 longitudinally, and measures 12-18 p. in length. There is a 

 rounded flat surface on which is a sucking disc with raised edge 

 and convex surface and which terminates in two flagella. Three 



1 Bulls. 166 and 168, Agricultural Experiment Station of the Rhode 

 Island State College, U.S.A., 1916. 



