ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
297 
Size-variation in Trypanosoma lewisi. — W. H. Taliaferro ( Proc . 
Nat. Acad. Sci ., 1921, 7, 138-43). This flagellate is a non-pathogenic 
blood-parasite occurring in various species of rats, and disseminated by 
the rat flea. It reaches an “ adult ” stage in its development in the rat 
in about twenty-five days after it appears in the blood. Once this 
stage is reached there is practically no division or growth. Because of 
the elimination of growth factors, the organisms show a very low 
coefficient of variation in “pure line” infections, provided they are 
measured after the “ adult ” stage is reached. These facts make T. lewisi 
a very favourable organism in which to study size-variation. J. A. T. £3 
Binary Fission in Callodictyon triciliatum. — R. C. Rhodes 
{Univ. California Publications , Zoology , 1919, 19, 201-74, 8 pis., 
4 figs.). This is one of the simplest Polymastigotes in structure and 
mitosis. The fission begins with an unequal constriction and differential 
division of the primary karyosome of the vesicular nucleus into a macro- 
karvosome and a microkaryosome, the latter alone functioning directly 
Laterosulcar view of Callodictyon x 1700, showing vacuolated! cyto- 
plasm, sulcus, vesicular nucleus, karyosome, two basal granules, 
four flagella. 
in the formation of the prophase skein, which! originates by the succes- 
sive segmentation of the microkaryosome into two crescents and four 
terminal knobs. These crescents split longitudinally, producing eight 
or seven terminal knobs which are the elements at least of chromosomes. 
Coincident with the beginning of the segmenting skein, there is formed 
around the microkaryosome a kinetic membrane which expands till 
commensurate with the nuclear membrane. In the final prophase there 
