238 RESEARCH IN PROTOZOOLOGY 



through genes arranged in linear aggregates to form chromo- 

 somes? If not, are there genetic chromatin particles which divide, 

 though not while aggregated in linear chromosomes ? 



5) If Kofoid's as yet unpublished studies of the neuro-motor 

 complex in Opalina ohtrigonoidea are correct, and if there are 

 homologous structures in the binucleated genera, what is the be- 

 havior of each element in this complex during the period of 

 emphasis upon sexual phenomena ? 



6) If, as Metcalf described, the ectosarc and endosarc spherules 

 greatly diminish in number, or wholly disappear, by the time the 

 gametes are fully formed, from what source and in what way is 

 each kind of these cytoplasmic inclusions redeveloped ? What light, 

 if any, does the behavior of these bodies throughout the life-cycle 

 cast on the problem of their nature and function? Does their pres- 

 ence during the phases of vegetative emphasis and their great 

 diminution or complete absence during the phases of sexual repro- 

 ductive emphasis indicate their special association with nutrition? 

 Are all of the two, three or four sorts of these bodies alike in their 

 relations to these phases of the Hfe-cycle? 



7) The growth of the zygote to the adult should be followed for 

 each genus and for most or all subgenera, and such study should 

 include the numerous changes of internal structure and the re- 

 markable changes of external form, especially the series of changes 

 by which each ( ?) species starts at the bottom, as a Protoopalina 

 of primitive type, and climbs its own ancestral tree to reach its 

 adult generic and specific character {Cf., Metcalf, 1926). 



III. HOST SPECIFICITY {Cf., also the section physiology) 



Metcalf 's review of the host-parasite relations among the 

 OPALiNiD^ showed a general, though not sharply exact, relation 

 between parasite genus or subgenus and host family, or in a few 

 cases host genus. The outlines of these relations are somewhat 

 vague, for there has been spreading of parasite groups to other 

 than their apparently original host groups, especially in the case of 

 certain unusually hospitable hosts, such as Bufo. Metcalf (1909) 

 showed that many, and probably all, species of tadpoles in Europe 

 can be infected by the cysts of many, probably of all, species of 

 European opalinids, and that the tadpoles remain for months in- 

 fected by apparently healthy parasites. Yet in the adult anura 

 the opalinids are restricted to a limited and characteristic host dis- 



