16 University of California Puhlications in Zoology [Vol. 18 



be called a pseudosynaptic phenomenon. There is no evidence that a 

 true synapsis occurs in any premitotic phases observed by me, more- 

 over, thus far no sexual reproduction has been discovered in Giardia. 

 Since, however, each chromosome seems to show a tendency in this 

 stage in ordinary vegetative mitosis to fuse with the corresponding 

 chromosome of its sister spireme strand, this relationship is strictly 

 one devoid of all true synaptic relations, and so can be looked upon as 

 wholly pseudosynapsis. 



Metaphase. 



The four chromatinie masses now at the equator of the spindle 

 appear to divide by transverse constriction through the center of each 

 mass (pi. 1, fig. 8; text-fig. J) ; the division is equal. It results in 

 the re-formation of eight chromosomes, two each from the four masses 

 formed from four chromosomes which had previously split and then 

 come together and fused. But, as has been said before, this apparent 

 transverse division of these four chromatinie masses is not true trans- 

 verse fission, but is rather an end-to-end separation, the completion 

 of a division along a longitudinal plane which is identical with the 

 plane of fusion of the two chromosomes. 



Again the chromosomes seem to be of uniform size (pi. 2, fig. 9) 

 and there is evidence here of their recent separation from other 

 chromosomes (pi. 2, fig. 9, left nucleus). For convenience we may 

 consider the chromosomes in this nucleus in the right and left hemi- 

 spheres. The two chromosomes above the equator in the right hemi- 

 sphere were probably separated from the two chromosomes below the 

 equator in the same hemisphere. Likewise the two chromosomes above 

 the equator in the left hemisphere were separated from the other two 

 chromosomes below the equator of the same hemisphere. It is possible 

 that these four chromosomes in the left hemisphere which are farther 

 separated from each other than those in the right hemisphere are the 

 upper chromosome pairs, and that, as in previous stages they were 

 formed first because of their proximity to the centrosome, so here, 

 not for the same reason, but because of their holding on to their prop- 

 erty of priority of change, they have been the first to become separated 

 and already have migrated farther than those in the right hemisphere. 



Anaphase 



This phase is noted by the migration of the chromosomes to the 

 poles of the spindle. The beginning of this phase shows the individual 

 chromosomes near each other subsequent to the division in the meta- 

 phase (pi. 1, fig. 9; text-fig. M). Often inequality of nuclear changes 



