478 Woo levy.—-Meiotic Divisions in the Micro spore 
the determination of the true forms and shapes of chromosomes, and it was 
found that the photograph bears a striking resemblance to the nucleus as 
seen in the microscope and as figured with drawing accompanying this paper. 
(Compare Text-fig. with Fig. 17.) 
The bivalent chromosomes which result from cross-segmentation con¬ 
tinue to shorten and thicken until they take the form as shown on the 
spindle plate (Fig. 21). They can be found assuming all the different 
shapes which have been described for them and in many different arrange- 
Text-fig. Photograph of plastina model of the same nucleus from which 
Fig. 17 on PI. XXII was drawn. 
ments. Figs. 16 to 20 show different shapes in which the chromosomes 
appear during this segmented stage. Some nuclei show bivalents of different 
lengths and widths (Figs. 17, 18, 19, and 20). Fig. 18 shows one bivalent 
which is bent back upon itself. Fig. 19 shows one portion of the segmented 
thread which is curved twice, but the limbs are not yet tightly wound about 
each other (Figs. 17 and 18), while others remain in ring-shaped forms. 
Farmer and Digby (T 3 ) have discussed the possible significance of the 
different sizes of chromosomes and the constancy of this variance in any one 
