PHYSIOLOGICAL ACTIVITIES OF THE PROTOZOA 



91 



from the free half, while in still other cases it is discarded before divi- 

 sion, and, as in copromonas, each daughter cell creates a new one 

 (Fig. 28). Similarly with the infusoria, some forms like paramecium, 

 colpidium, etc., have a cover of uniform cilia which are retained during 

 the act of division; indeed, the organisms swim vigorously throughout 

 the entire process, but in other forms, as Euplotes patella, oxytricha, 

 stylonychia, etc., the more complex motile organs are discarded and 

 formed anew by the daughter cells (Wallengren) (Fig. 29). 



jln the flagellate Noctiluca miliaris (Fig. 30), the division is accom- 

 panied by very complicated nuclear changes, and a division figure is 

 formed which recalls the mitotic figure of the metazoan cells. The 

 chromatin in the ordinarv conditions of the cell is contained in a few 



FIG. 29 



Euplotes patella in division. The macronucleus is not quite divided, the daughter 

 nuclei being connected by a delicate strand. 



large chromatin reservoirs or karyosomes; these disintegrate prior to 

 division, and the granules thus formed collect in lines, the chromo- 

 somes, which are oriented toward one pole of the nucleus. At this 

 pole, but on the outside of the nuclear membrane, lies a large centro- 

 some or division centre, which divides during the time of disintegra- 

 tion of the karyosomes and forms a central spindle between the two 

 halves. The nuclear membrane next disappears in the region between 

 the chromosomes and the spindle, but is retained elsewhere, and 

 special spindle fibres grow out from each of the division centres and 

 become attached to the ends of the chromosomes. The division 

 centres then move apart and the chromosomes are drawn asunder, 

 each having divided through the middle. 



