412 DORIS L. MACKINNON. 
measured. (Before sectioning, I drew the outlines of the 
cyst with a Zeiss drawing-apparatus, and filled in also the 
nuclear outlines, when I could see them distinctly. Fre- 
quently I measured the nuclei at this stage, to act as a check 
on later measurements in section). The nuclei, when sec- 
tioned, I measured under oil-immersion. As in most cases 
the primary karyokinesis had been finished and the nuclei 
had begun to become heteropolar, I took measurements in 
two directions. This brought out an average, in the warmth, 
of 16°64 x 13°8 u, and, in the cold, of 1524x148. That 
Wravs 
Text-rics. lw anp 18. 
Four primary cysts from culture B 9, arranged so as to show the 
comparative dimensions of cyst and nucleus in the warmth, 25° C. 
(darker line), and the cold, 10° C. (thinner line). Drawn with Zeiss 
drawing apparatus, oc. 3, obj. 7 (microscope tube of normal tength), 
at the level of the work-table. 
is to say, the mean diameter in the warmth was 15:2 pe, and 
in the cold 14°8 ». Nuclei measured previous to the primary 
karyokinesis gave, in the warmth, an average diameter of 
20°2 uw, and in the cold of 195 4. In fact, the difference 
in size between nuclei from warm and cold cultures was 
scarcely appreciable; those from the cold culture were very 
slightly the smaller. In comparison with the considerable 
size-differences between the cysts themselves, this agreement 
in the dimensions of their respective nuclei is rather striking. 
Though fairly exact correspondence in nuclear dimensions 
