126 LOUISE B. WALLACE. 



always directed toward that part of the cell which contains the 

 greatest amount of cytoplasm and in which the centrosome lies. 

 This pole has been called by Montgomery the distal pole. The 

 closed ends of the spireme loops are directed toward the opposite 

 or central pole. The same relative position of the loops, the 

 accessory chromosomes and the centrosome is retained through- 

 out the growth period and gives striking evidence of cell polarity. 

 At a slightly later stage the accessory chromosomes seem to be 

 simulating the structure of the spireme to a limited degree. 

 They temporarily lose their compact form, become distinctly 

 granular and extend in length over about two thirds of the 

 diameter of the nucleus (Fig. 15). Gradually they shorten 

 again and conjugate side by side, the union usually first taking 

 place at the end directed toward the central pole and progressing 

 toward the distal pole (Fig. 16). Cases are found in which the 

 union begins simultaneously at the two extremities, giving a 

 ring-like form. After the union is completed they appear as a 

 single mass when viewed either in longitudinal or cross section 

 (Figs. 17 and 18). Whether in this conjugation a complete 

 fusion of the two elements occurs or whether it is merely a close 

 approximation, I am unable to say, but soon the single mass is 

 again split into the two characteristic rods. 



When the longitudinal split in the spireme has reached its 

 widest extent, some of the loops still extend nearly across the 

 nuclear cavity but later they begin to draw down toward the 

 distal pole. As the shortening continues, the longitudinal split 

 becomes less and less evident but indications of it can be detected 

 at a late stage. Judging also from the subsequent history I believe 

 that the split persists, being merely lost sight of in the close 

 approximation of the two moieties during the process of contrac- 

 tion (Figs. 19-21). In the late prophase, the loops of the spireme 

 not only shorten but bend to an acute angle to form V-shaped 

 chromosomes which then open out into double V's (Fig. 22). 

 The chromatin of these is in a more or less granular condition 

 and leaving their former position at the distal pole they are dis- 

 tributed through the nuclear cavity. The rod-like accessory 

 chromosomes remain unchanged both in form and in position. 

 Soon the nuclear membrane disappears, the ordinary chromo- 



