352 BIOLOGY OF THE LABORATORY MOUSE 



anterior flagella and two posterior flagella which arise from axonemes. 

 There are two nuclei situated near the anterior end. Wenyon (43) describes 

 the trophozoite in the intestine as being from 4 /i to 7 )U in length, while a 

 larger form occurring in the caecum measures as much as 10 /z. The cysts are 

 oblong, measuring 6 ^t to 7 ^t in length and 3 ^ to 4 /x in breadth. In the cysts 

 nuclear division occurs, and multiplication is also by longitudinal fission 

 of the trophozoite. 



Fig. 136. — Flagellates from the intestine of the rat as seen when alive, i, Giardia 

 niiiris; 2, Hcxamita muris; 3, Tricltomonas muris. {After Hegner.) 



Giardia muris (grassi, 1879). — According to Hegner (20) G. muris 

 occurs in a considerable portion of laboratory rats and mice. The tropho- 

 zoites live in the small intestine while the cysts can be found in the caecum 

 and the colon or in the feces (Fig. 136). 



The trophozoite is a flattened, pear-shaped, bilaterally symmetrical 

 organism measuring on the average 9.8 jx in length and 6.75 yu in breadth. A 

 large ventral anterior sucker attaches it to the intestinal epithelium. Two 

 nuclei and a pair of blepharoplasts are located in the anterior region. From 

 the blepharoplasts arises a pair of flagella which pass anteriorly and after 

 crossing near the extreme anterior margin pass laterally to emerge one on 

 either side of the organism. A second pair of flagella which also arise from 

 the blepharoplasts pass posteriorly to emerge laterally toward the posterior 

 end of the body. A pair of axostyles (single, according to Kofoid and 



