RESEARCH PROBLEMS IN THE OPALINID^ 241 



these ANURA whose adults are uninfected? b) Remove gonads 

 from male anura and observe effects, if any, upon the behavior of 

 the opalinids. c) Do the same with the gonads of female anura. 

 d) Treat both sexes in a similar way, only cut, or tie off, the vasa 

 effcrenfia and the oviducts, ej If the opalinids show different 

 behavior in hosts whose genital ducts have been ligated or cut from 

 that which they show in hosts whose gonads have been wholly 

 removed, follow the study further by introducing into such un- 

 sexed hosts gonads from other species which normally carry dif- 

 ferent species of opalinids from those occurring in the operated 

 hosts. Make reciprocal crosses in this way. Such experiments may 

 give some light upon, first, the nature of the stimulus which in- 

 duces opalinids to encyst at their presexual period, and whether 

 these stimuli are internal or environmental, and, second, upon the 

 control over host-parasite specificity in infection. 



9) In thyroidectomized tadpoles of anura which carry opaH- 

 nids of a different appearance (stage of development ; Cf., ]\Ietcalf, 

 1926) in the adults and in the tadpoles, observe if in these tadpoles 

 with delayed metamorphosis the opalinids complete their usual 

 development. 



V. SOURCES OF SUPPLY AND METHODS 



For most studies the binucleated species are much to be pre- 

 ferred. The body is less crowded with nuclei ; the nuclei are larger, 

 their chromosomes are fewer in number, if there be any connection 

 between a particular nucleus and any of the cytoplasmic inclusions 

 (Cf., Kofoid's paper as yet unpublished) these relations should be 

 more readily determined ; indeed the whole internal structure is 

 less crowded and easier to study. 



IMaterial of the binucleated genera, Protoopaliua and Zellcriclla, 

 is not available for study in the northeastern part of the United 

 States, nor is it abundant in the southeastern region. In the west 

 and southwest several species of Protoopaliua occur, and Zclleri- 

 ella can be had in the southwest. The author of this paper, with 

 the cooperation of a number of zoologists in different parts of the 

 country, is making attempts to introduce and naturalize the Euro- 

 pean Fire-Toad {Bombina boinbina, commonly called Bombinator 

 igiieus) which harbors Protoopalhm intcstinalis and P. caudata, 

 species especially favorable for study. Within a year the probable 

 success or failure of these attempts should be known, and report 



