THE PROTOZOA AS PARASITES OF MAN 



159 



the hollow side, an undulating membrane, one contractile vacuole in the 

 hinder part of the body, and a remarkable permanent anus, lined with 

 ectoplasm, at the hind end. The related N. faba has been found in the 

 intestine of a man suffering from dysentery, but it is doubtful whether 

 it was the cause of the disease. 



More numerous and conspicuous than either of these is Opalina 

 ranarum, a flat, oval, pale-straw-coloured ciliate of very large size 

 (i mm. long), uniformly covered with equal cilia, and without mouth, 

 peristome, contractile vacuole, or trichocysts. It has many nuclei, 

 unlike those of other Ciliata in being all of one kind. The life-history 

 is also very unlike that of other Ciliata. Nuclei and cytoplasm divide 

 independently (the latter alternately in a longitudinal and a transverse 

 direction), and during the greater part of the year keep pace with one 



Fig. 99. — Ciliata from the rectum of the frog. 



A, Opalina ranarum ; B, Balantidium entozoon ; C, Nyctotherus cordiformis. 



an.. Anus; c.v., contractile vacuoles; ec, ectoplasm; en., endoplasm ; g., gullet; 



meg:, meganucleus ; mi. , niicronucleus ; nu., nuclei ; v., vestibule or peristome. 



another and with growth, so that the appearance of the mature animals 

 remains the same ; but in the spring the division of the cytoplasm 

 gains, so that small individuals with 3-6 nuclei result. It is said 

 that at this time a portion of the chromatin of the nuclei passes in 

 granular or "chromidial" form (p. 83) into the cytoplasm, where it 

 condenses to form new nuclei while the old ones perish. The little 

 individuals now encyst, casting out from each nucleus two successive 

 masses of chromatin which are destroyed. The cysts are passed by 

 the frog into the water and there swallowed by tadpoles, in which they 

 hatch and their cytoplasm divides to form uninuclear gametes. These 

 conjugate, and the zygote encysts. From the cyst emerges a uni- 

 nuclear ciliate which grows into the adult. During the whole process 

 cilia are lost only in the zygote cyst. A comparison of this life- 



