riiE rnh'xoMKXA of maturatiox rx pmnozoA ig7 



tion process. l(s work is doiio, and, like tho soinatio cells of the 

 ineta/.oa, it dies. The iniiToiiucleus, on the other hand, after Iving 

 dormant so far as the vegetative fnni'tions of the cell are concerned, 

 now begins its germinal activity. It moves away from the macronn- 

 oleus, where it usnally lies in a cleft in the substance of the macro- 

 nucleus, and begins to swell. It contains two substances: one, located 

 Jit one pole of the nucleus, is the substance of the di\-ision centre, and 

 gives rise to the libers of the spindle tigure, so that in it rests the poten- 

 tial energ\' whit'h is later converteil into the kinetic energy of division. 

 The other substance is chromatin, which is concentrated at this time 

 in a number of granules closely packed against the division centre. 

 The nucleus then elongates by fragmentation of the chromatin gran- 

 ules, the fragments arranging thenisehcs in lines radiating out from 

 the tlivision centre. They correspond to the itliochromidia of the 

 rhi/.opod cell, but are now assuming definite form, the irregular and 

 distributed idiochromidia of the more primitive organisms being 

 replaced here by the more delhiite chromosomes. The elongation of 

 these lines of chromatin eontinnes until the nucleus is an enlarged, 

 narrow structure many times longer than the resting nucleus. The 

 intranuclear division centre, which is concentrated at one end of the 

 mu'leus, likewise increases in size (^Fig. ~'2). 



The micronueleus next becomes curved in such a way that the two 

 ends are brought close together, forming a distinct crescent, with the 

 long lines of chromatin uniting to make a liranched network extending 

 from tip to tip, while the division centre, now nuicli enlarged, moves 

 toward the centre of the crescent. The chromosomes of the first 

 division iii;in'e are formed by the transverse division of the elongated 

 lines of chromatin granules, but, owing to the net formation and 

 association side by side, these short fragments are each double, a 

 lono'itudinal split appearing in each. All of tlie chromatin is thus 

 utilized and an uncountable number of chromosomes arc thus formed. 

 The siibstancc of the division centre then diffuses through the nucleus 

 in a kind of flowing division and the two poles of the Hrst maturation 

 spindle are formed by the accnnuilatiou of this material at the opposite 

 sides of the nuclens. With this flow the chromosomes are divided, so 

 that when the spindle is entirely formed the datighter halves of the 

 chromosomes are separated and now lie end to end in the Si>-<.\illed 

 ana[iliase stage of division (^Fig. "-. OV (.See Calkins and L'nll (^'t)S"i for 

 the details of this spindle fornration."! 



The nucleus then divides by constriction through the middle and the 

 first two maturation nuclei are the result. Kach of these next ili\ii.les 

 a^-ain, the process of division being identical witli that described 

 above and four luaiuration mielci are formed. Two of these immedi- 

 atelv bci^in to degenerate, while a third follows suit shortly after, the 

 fourth alone dividinix a third time. Here the chromatin is not divided 



