"I OPALINA 269 



It will be noticed that, in the present instance, conjugation 

 is not a process of multiplication : it has been ascertained 

 that during the time two infusors are conjugating each 

 might have produced several thousand offspring by con- 

 tinuing to undergo fission at the usual rate. The importance 

 of the process lies in the exchange of nuclear material 

 between the two conjugating individuals : without such 

 exchange these organisms are said to undergo a gradual 

 process of senile decay characterized by diminution in size 

 and degeneration in structure. 



Some ciliate Infusoria axe parasites. Parasites are organisms 

 which live in association with other organisms, the ready- 

 digested food of which they utilize or even nourish them- 

 selves from the tissues of the forms they infest. It will be 

 interesting to compare Paramoecium with an Infusor which 

 lives in the intestine of the common frog, and is known 

 as Opalina ranarum. 



Opalina has a flattened body with an oval outline (Fig. 71, 

 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 ; the cilia are 

 equal-sized and uniformly arranged in longitudinal rows over 

 the whole surface. 



On a first examination no nucleus is apparent, but after 

 staining, a large number of globular nuclei can be seen (b, nu) : 

 these nuclei multiply within the body of the infusor. 



The presence of numerous nuclei in Opalina is a fact 

 worthy of special notice. The unicellular organisms we have 

 studied are uninucleate as well as unicellular (compare, 

 however, Fig. 67, B) : the higher animals consist of numerous 

 cells each with a nucleus: Opalina, on the other hand, is 

 multinucleate but its protoplasm is undivided, so that it 



