GENUS: GIAEDIA 



699 



two pairs. The writer has already expressed it as his opinion that the 

 flagellate possesses two pairs of anterior blepharoplasts, and he believes 

 that when division is taking place there actually occur four pairs of 

 anterior blepharoplasts. Boeck describes the changes in the nucleus as 

 taking place in the following manner (Fig. 295) : The fibril, which is said 

 to connect the granule on the anterior end of the nuclear membrane with 

 the karyosonie, becomes extended to the opposite pole of the nucleus. 

 The karyosome then becomes more irregular in shape, and finally divided 

 into eight chromosomes. Meanwhile, the granule on the anterior end of 



Fig. 295. — Mitotic Division of Nucleus of Giardia microti { x ca. 7,300). (After 



BoECK, 1917.) 



1. Ordinary resting nucleus with karyosome cormected with centrosome by a fibril. 



2. Karyosome has elongated. 



3. Elongated karyosome has split longitudinally, and each half is dividing into four chromosomes. 



4. Division of each half of karyosome into four chromosomes is complete. The centrosome has 



divided, and the two daughter centrosomes are connected by a fibre (paradesmose). 



5. The eight chromosomes have united to form four double chromosomes at the equator of the 



spmdle. The paradesmose is no longer visible. 



6. The four double chromosomes have divided to form two groups of four which move towards 



the poles of the spindle. 



7. Division nearly completed; chromosomes fused. 8. Completed division. 



the nuclear membrane has divided, and one half migrates over the surface 

 of the nuclear membrane to the opposite pole of the nucleus. It remains 

 connected with the other half, which retains its anterior position, by 

 a centrodesmose which lies on the surface of the nuclear membrane. 

 Between the two granules, which are functioning as centrosomes, a spindle 

 is formed within the nuclear membrane, and upon the fibres of the spindle 

 the eight chromosomes arrange themselves. The chromosomes are 

 described as four pairs of homologous chromosomes, and the individuals 

 of each pair become closely associated to form four double chromosomes 

 at the equator of the spindle. One chromosome of each pair now moves 



