LESSON XI 



OPALINA 



THE large intestine of the common frog often contains 

 numbers of ciliate Infusoria belonging to two or three 

 genera. One of these parasitic animalcules, called Opalina 

 ranarum, will now be described. It is easily obtained by 

 killing a frog, , opening the body, making an incision in the 

 rectum, and spreading out a little of its blackish contents in 

 a drop of water on a slide. 



Opalina has a flattened body with an oval outline (Fig. 

 25, A, B), and full-sized specimens may be as much as one 

 millimetre in length. The protoplasm is divided into cortex 

 and medulla, and is covered with a cuticle, and the cilia are 

 equal-sized and uniformly arranged in longitudinal rows -over 

 the whole surface (A). 



On a first examination no nucleus is apparent, but after 

 staining a large number of nuclei can be seen (B. nu\ each 

 being a globular body (c, i), consisting of achromatin sur- 

 rounded by a membrane and containing a coil or network 

 of chromatin. These nuclei multiply within the body of 

 the infusor, and in so doing pass through the various 

 changes characteristic of karyokinesis or indirect nuclear 

 division (compare Fig. 10, p. 64, with Fig. 25, c) : the 



