OF THE ALHIENTARY TRACT 183 



motionless organism. In that state the flagella may 

 be seen to hang as long delicate fibrils, one pair from 

 forward on the outer border of the sucker, two pairs 

 from near the midline posterior to the sucker, and the 

 fourth pair from the tail. 



In motion the body vibrates rapidly with the ac- 

 tion of the flagella and it frequently doubles upon 



Fig. 27. — Giardia iritestinalis. 



Trophozoite and cyst as drawn from living unstained specimens. 

 X 2000. 



itself. After all other motion has ceased, the fla- 

 gella which extend backwards along the ventral mid- 

 line may continue to undulate. 



In fresh unstained specimens the cysts are readily 

 recognizable to one on the search for them, although 

 they vary in number in the same individual and may 

 be absent at times. There is some belief that they 

 appear periodically as a habit of life of the organism. 



