PHYSIOLOGICAL DEGENERATION IN OPALINA. 633 



Physiological Degeneration in Opalina. 



By 



€. Clifloid Dobell, B.A., 



Scliolar of Trinity College, Cambridge. 



With Plate 38 and 2 Text-fisures. 



Introduction. 



In many respects Opalina ran arum, Park, and Val., is 

 one of the most interesting of tlie ciliated Protozoa. Although 

 its adult appearance has been familiar to all zoologists for a 

 long time, it is only in the course of the last year that its 

 interesting life-cycle has become fully known. We owe this 

 knowledge to Neresheimer, who has, however, only given us 

 a preliminary account of his important researches. His full 

 paper will be awaited with much interest. 



It will be unnecessary for me to give a detailed description 

 of this very common species. But I would remind the reader 

 that it is a large, multinucleate, holotrichous form found in 

 the large intestine of our common frog and toad (Rana 

 temporaria, L., and Bufo vulgaris, L.). The nuclei may 

 be regarded as cousisting of meganucleus and micronucleus 

 fused to form a synkaryon. For an account of the life-history 

 the reader is referred to accounts already published, but 

 more especially to the memoirs of Zeller and Neresheimer. 

 It will be necessary for me to give a brief account of the 

 earlier part of the life-cycle, however; that is to say, of the 

 part prior to encystment, which takes place in the adult host. 



