28 MARGARET C. FERGUSON 



As the spindle-tibers press into the nuclear cavity, the chro- 

 mosomes take up their position at the equatorial plate. They 

 are now verv regular in outline, apparently homogeneous, and 

 the X. Y, V, O, etc., forms can still be clearly distinguished 

 (hg. 24, plate III). Each segment is oriented with its longer 

 axis perpendicular to the axis of the spindle, the free limbs ex- 

 tending outward. The spindle-fibers are attached at one ex- 

 tremity of the parallel rods, and ordinarily at or near the point 

 of union of the constituents of the dual chromosomes. In the 

 Y-shaped chromosomes the achromatic threads may become at- 

 tached at the point where the two limbs become free or at the 

 free end of the fused chromosomes, but, whatever the shape of 

 a segment, the spindle-fibers are never attached at the extremi- 

 ties of its free limbs. 



The line of cleavage at the equatorial plate is not such as 

 to separate the two chromosomes but is rather such as to effect 

 a longitudinal splitting, the two half chromosomes of each pair 

 passing together to opposite poles. During metakinesis the 

 daughter-chromosomes become very irregular in outline and in- 

 crease much in size, the half chromosomes apparently exceeding 

 in volume the undivided ones (figs. 25-2S). This augmentation 

 of the segments maybe due to actual addition of new substance, 

 but from the fact that in the telophase they are unquestionably 

 smaller than in the late prophase, it is probable that this is 

 merely an amplification without actual or permanent growth. 

 The parts of the spireme separated during the longitudinal fis- 

 sion following synapsis have so completely fused again that 

 they are now disunited with difficulty. The appearance of the 

 dividing chromosomes indicates that they are being subjected 

 to great strain. Under this tension they are flattened out and 

 rendered irregular in outline ; the irregularities result from the 

 unequal stretching of the chromatic substance at different 

 points, just as a poor rubber band when greatly extended be- 

 comes more or less moniliform. The complete separation of 

 the half chromosomes may sometimes be greatly delayed, when 

 the stretched segments extend nearly the entire length of the 

 spindle, the achromatic figure being almost obscured, in some 

 instances, by the chromosomes (figs. 25, 26, 2S and 29). That 



