454 



SPECIFIC MICRO-ORGANISMS 



Opalina Ranarum. — This is a common, parasite in the in- 

 testine (cloaca) of the frog. It reaches a large size, 600 to Soo/j. 

 in diameter, is flattened and somewhat irregular in outline. The 

 ectoplasm is striated and there are very many nuclei in the in- 

 terior of the cell. In the springtime, as the frogs enter water to 

 spawn, the parasites divide rapidly and give rise to cysts 20 to 40/^ 

 in diameter. These escape into the slime and are ingested by 

 the growing tadpoles. In the cloaca the cells escape from the 

 cysts. They are differentiated into male and female gametes and 



A B 



Fig. 21S. — Opalina ranarum, showing the numerous vesicular nuclei. A, Ordinary 

 form. B, Dividing form. {From Doflein after Zeller.) 



fuse to^ form one cell which grows and multiplies in the developing 

 frog. 



Balantidium Coll. — This parasite of the human intestine was 

 described by Malmsten in 1857. Its normal habitat seems to 

 be in the large intestine of swine, where it is commonly found in 

 large numbers. The cell is a short oval, 50 to 70/1 wide and 

 70 to loofj. long, rarely larger. Jts surface is covered with active 

 cilia, and there is a short oral groove at the anterior end. The 

 cytoplasm contains drops of fat and food vacuoles, often red 

 blood cells and leukocytes of the host. The principal nucleus 



