6 BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



tact when the alcohol in which they and the host are preserved 

 weakens afterwards sufficiently to allow the tissues of the host to 

 become very flabby. 



A word of explanation seems due in view of the absence of a gen- 

 eral summary of the conclusions reached in this paper. Section 2 

 is itself a summary of the structure and life history of a sample 

 species; section 3 deals with detailed taxonomy and can not well be 

 summarized beyond the final classificatory table; sections 5 and 6 

 are themselves in a measure summaries of the data in the earlier parts 

 of the paper ; section 7 contains summaries of the indications found 

 in the different phases of its discussions; and section 8 summarizes 

 under each Anuran family the infection data contained in its long 

 table. The nature of this paper is such that it is little better adapted 

 to summarizing than would be an encyclopedia. The table of con- 

 tents shows the nature of each section of the paper, and the index 

 will guide one promptly to the data and discussions upon any of its 

 points. The author is unable to provide a brief statement of the 

 data, indications, and conclusions, perusal of which might serve as 

 a substitute for reading the paper. 



2. THE STRUCTURE AND THE LIFE HISTORY OF PROTOOPALINA 



INTESTINALIS. 



The significance of much of the data in this paper might be ob- 

 scure to one who had not in mind the chief phenomena of the struc- 

 ture and life cycle in the Opalinidae. For this reason it seems im- 

 portant to give here an outline of both the structure and the life his- 

 tory of a sample species. This seems the more worth while since no 

 accurate succinct account has been published. Zeller does not de- 

 scribe the sexual phases of the life cycle and is misled as to the en- 

 cysted phase, and Neresheimer's account includes some statements 

 which later studies have failed to confirm. My own account of the 

 life history, based on the study chiefly of two binucleated species, 

 omitted certain phenomena described by Neresheimer and interpreted 

 by him as presexual degeneration of the nuclei and the formation of 

 secondary generative nuclei from chromidia. In some of the species 

 observed in the present study I think I have some of the phenomena 

 observed by Neresheimer, but their interpretation is still doubtful. 

 Neresheimer's and the author's previous accounts are too detailed for 

 the most convenient use by those interested in the general course of 

 events rather than the minutiae. 



Protooyalina infesthialis, the first discovered of the binucleated 

 Opalinidae, has been reported as parasitic in Bonibina hombina 

 [^^ Bomhinator ir/neus^^], Bomhina pachypa \^^ Bomhinator fachy- 

 pw5"], Discoglossus pictVrS, Pelohates fuscus, P. cultj'ipes, Bufo cola- 



