236 RESEARCH IN PROTOZOOLOGY 



upon the appearance of abnormalities. The sensitiveness of the 

 macrochromatin to unaccustomed conditions would serve as an 

 important index if opalinids could be reared, success fully outside 

 the host. The study of these abnormalities, the circumstances of 

 their appearing and a comparison with the diverse appearances and 

 behavior of the macrochromatin during the normal life-cycle, may 

 help to interpret the normal changes. The individuality of the 

 macrochromosomes of binucleated species only (described by Met- 

 calf ) may well be studied by another observer, since such a condi- 

 tion would naturally seem in itself improbable, b) The genetic 

 chromosomes, strings of beads, somewhat as in Paramecium, need 

 minute study. Is their number always the same as that of the 

 macrochromosomes in binucleated species (as Metcalf found to 

 be the case in two species of Protoopalina and one species of 

 Zelleriella, not demonstrated in multinucleated genera) ? The 

 lengths of the genetic chromosomes and the numbers of their con- 

 tained granules differ between the chromosomes and, at least in 

 some species, the numbers of granules in different chromosomes 

 differ by a measure greater than the margin of error in the counts 

 in favorable material. Are these differences constant in different 

 nuclei of the same species, and can individual genetic chromosomes 

 thus be distinguished and followed, as Metcalf claimed was true 

 for the macrochromosomes in the vegetative phases of the life- 

 history in two species of Protoopalina? 



6) Mitosis. Splitting of chromosomes, both macro- and micro-? 

 At what stage of the mitotic cycle does splitting occur, if at all? 

 Are the phenomena consistent with any Mendelian division and 

 distribution of genes? 



7) The plasmosome nucleolus, its nature and its relation to the 

 cell physiology? Does it have the peculiar behavior in cell-division 

 described by Metcalf (1909) ? From what source does it arise in 

 the second of the two daughter nuclei after cell-division? 



8) The centrosome (wholly absent according to Metcalf) ; can 

 its homolog be identified ? 



9) The mitotic spindle; is it composed of chromatin threads, or 

 achromatin, or are there both chromatic and achromatic threads 

 (C/., Metcalf, 1909) ? 



The fact that something of nuclear structure, including the 

 chromosomes, some of the mitotic spindle fibers and the course of 

 mitotic division, can be made out in the living animal suggests 



