88 PEACTICAL PABASITOLOGY 



waves which pass over a field of corn. These movements should be 

 carefully studied, carragheen (which has been previously swelled in 

 normal saline) being added wherever necessary, though as a general 

 rule the bowel-contents will be sufficiently thick without it. The cilia 

 are arranged in longitudinal rows, corresponding to a fine longitudinal 

 striation of the surface of the parasite. There is no cytostome, 

 nutrition taking place by endosmosis. There are also no contractile 

 vacuoles. The Opalina resemble the true Infusoria in possessing a 

 ciliated exterior, but they differ from them in the method of their 

 reproduction 1 and in the absence of anything resembling nuclear 

 dimorphism. Three varieties of Opalina are found in indigenous frogs. 

 They are as follows : 



"'/ ^ 



FIG. 26. Infusoria from the large intestine of Rana temporaria (original), a, Balan- 

 tidium entozoon. 6, Nyctotherus cordiformis. c, Opalina ranarum. Magnified, a and b> 

 315:1; c, 125 : 1. 



Opalina ranarum (in Eana temporaria). Much flattened in form ; 

 this parasite is about half as broad as it is long, the greatest breadth 

 being at, or just behind, the middle line. 



0. dimidiate (in E. esculenta). Spindle-shaped: about four times 

 as long as it is broad, the greatest breadth being anterior to the middle 

 line. 



0. zelleri (also in R. esculenta). Very clumsy in shape; at least 

 half as broad as it is long ; not nearly so much flattened as 



1 E. Neresheimer, ," Die Fortpflanzung der Opalinen," Arcli. f. ProtistenJcunde, 

 suppl. i, 1907, pp. 1-42. 



