122 OPALINA 



life, burdened with the necessity of finding food for itself, for 

 existence in the interior of another organism, on which in 

 one way or another it levies blackmail. 



Note the close analogy between the nutrition of an internal 

 parasite like Opalina and the saprophytic nutrition of a 

 monad (p. 39). In both the organism absorbs proteids 

 rendered soluble and diffusible, in the one case by the 

 digestive juices of the host, in the other by the action of 

 putrefactive bacteria. 



The reproduction of Opalina presents certain points of 

 interest, largely connected with its peculiar mode of life. It 

 is obvious that if the Opalinse simply went on multiplying, 

 by fission or otherwise, in the frog's intestine, the population 

 would soon outgrow the means of subsistence : moreover, 

 when the frog died there would be an end of them. What 

 is wanted in this as in other internal parasites is some mode of 

 multiplication which shall serve as a means of dispersal, or in 

 other words, enable the progeny of the parasite to find their 

 way into the bodies of other hosts, and so start new colonies 

 instead of remaining to impoverish the mother country. 



Opalina multiplies by a somewhat peculiar process of 

 binary fission : an animalcule divides in an oblique direction 

 (Fig. 25, D), and then each half, instead of growing to the 

 size of the parent cell, divides again transversely (E). The 

 process is repeated again and again (F), the plane of division 

 being alternately oblique and transverse, until finally small 

 bodies are produced (G), about -^-"FO mm. in length, and 

 containing two to four nuclei. 



If the parent cell had divided simultaneously into a num- 

 ber of these little bodies the process would have been one of 

 multiple fission : as it is it forms an interesting link between 

 simple and multiple fission. 



