34 JJniversiiy of Calif ornia Publications in Zoology [Vol. 20 



The loops or V-shaped chromosomes are gradually drawn by the 

 angle of the V towards the two ends of the paradesmose (pi. 3, 

 figs. 15, 17, 18). It is possible that each original loop is split length- 

 wise during this movement but the evidence for it is by no means 

 clear. During this process the loops shorten, thicken, and stain more 

 deeply, so that when they have finally parted (pi. 3, figs. 16, 20, 21) 

 they form chrysanthemum-shaped rosettes. 



The anaphase is brief and is also dominated by the stout parades- 

 mose, which continues to produce a one-sided, asymmetrical grouping 

 of the two groups of parting chromosomes and to modify the constric- 

 tion of the nuclear membrane so that it is also one-sided. The nuclear 

 membrane remains intact throughout the whole process of mitosis. 

 In the late anaphase constriction is completed, the nuclei separate 

 and move apart (pi. 4, fig. 22), stretching out the paradesmose be- 

 tween them a-s a result of the uncoordinated activities of the two 

 daughter neuromotor systems, which are attached to the nuclei by 

 their rhizoplasts. 



The telophase (pi. 4, fig. 36) ensues before plasmotomy. In it 

 the chromatin of the massed chromosomes rounds up in the central 

 mass and the clear zone reappears and the ellipsoidal form is resumed. 

 The paradesmose also fades away, and the centrosome merges with 

 the daughter blepharoplast which, by the shortening of the nuclear 

 rhizoplast, comes to lie closer to the nuclear membrane, thus bringing 

 the schizont back to the nuclear condition prior to mitosis. 



The process of mitosis in Trichomitus is similar to tliat in other 

 trichomonads in that the nuclear membrane remains intact through- 

 out the process, the extra-nuclear paradesmose arises between the 

 daughter centrosomes, and the duplication of the neuromotor system 

 proceeds from the centroblepharoplast and takes place prior to divi- 

 sion of the chromosomes. It differs in having a distinct separation 

 of centrosome and blepharoplast for a long period, in having a rigid 

 bar-shaped paradesmose, and in the large size and greater elongation 

 of the chromosomes. This higher specialization is conditioned by 

 crowded conditions of parasitic life in association with other parasites 

 of relatively complex organization. The conditions of locomotion in 

 this association and the excessive amount of stimulation consequent 

 thereon are causes conducive to the extraordinary development of the 

 neuromotor apparatus in Trichomitus and the resulting modifications 

 in mitosis. 



