THE PROTOZOAN LIFE CYCLE. 24! 



of the maturation process agrees with a remarkable exactness 

 with what occurs in many germ cells. The curious and enig- 

 matic crescent which the micronucleus forms during the early 

 phases of maturation, is the form assumed by the nucleus during 

 the stages of synapsis and contraction, and the first spindle 

 develops from this crescentic nucleus with its longitudinally 

 divided chromosomes in the form of heterotypical loops. The 

 condensed chromatin of the resting nucleus is first broken up into 

 many fine granules which become arranged in lines radiating 

 backwards from the intranuclear division center. The nucleus 

 elongates in the direction of these lines until it is seven or eight 

 times the original length. Then, with the growth of the division 

 center, the entire structure becomes crescent shaped and many 

 times the volume of the original micronucleus. The long lines 

 of chromatin appear to form a confused network, but in the con- 

 traction phase which follows shortly after the crescent, it can be 

 seen that these lines of chromatin are much thicker than they 

 were and distinctly double, and although not conclusively demon- 

 strated, the most reasonable interpretation regarding their origin 

 is that the long lines of chromatin unite side by side in a typical 

 parasynapsis. 



It has been customary to describe the pronuclei in Paramedum 

 as fusing while in the spindle form. In a general way this is 

 true, but it is only an elongated form assumed by the nucleus 

 at the time of this union, for the spindle at this time is in no 

 sense a mitotic spindle, the chromatin being in a finely divided 

 state and distributed throughout the nuclei. 



It has been generally believed that conjugation brings about 

 a renewal of vitality, a Verjiingung or rejeunissement according 

 to Butschli and Maupas, or an Erfrischung, to use a term sug- 

 gested by Weismann. This interpretation seems to be so obvious 

 on a priori grounds that experiments to prove it would appear 

 hardly necessary. In protozoa it is not rajuvenescence strictly 

 speaking but the formation of a new individual, and so also is it 

 in metazoa. It would seem to be easy enough to prove that 

 conjugation actually starts a new race from weakened individuals, 

 but singularly few experiments have been undertaken with this 

 object in view. Some that have been carried out by Miss Cull 



