160 THE CHROMOSOMES 



thin threads next assume the form of loops with their 

 free ends pointing toward one pole, e (bouquet 

 stage, also called the period of synapsis). At their 

 free ends the threads soon appear to meet in pairs, 

 d and e. Each pair, by the apparent fusion of its 

 threads, leads to the formation of a thick thread in 

 the form of a loop, /. Further condensation and 

 separation of the threads leads to the condition shown 

 in g. The thick double threads next show a length- 

 wise split, the halves being often twisted around 

 each other (diplotene stage) h. The pairs of threads 

 now begin again to become longer and to occupy 

 more of the interior of the nucleus as seen in i. The 

 eggs have grown larger meanwhile and the yolk 

 appears. As the nucleus grows still larger, keeping 

 pace with the growth of the cell, the chromosomes 

 begin to lose their staining capacity. Despite the 

 difficulty of tracing the chromosomes throughout the 

 remaining period, Marechal has succeeded in follow- 

 ing them, step by step. His drawings of the chro- 

 mosomes give the impression of the existence of a 

 central core or filament remaining, as show^n in 

 Fig. 44 i, j, k. Delicate loops and threads are 

 attached to this core and may be traced out into the 

 region of each side of the chromosome. During 

 these stages deeply staining balls of material, the 

 nucleoli, appear in the nucleus. Finally the chro- 

 matin threads begin to condense again and once 

 more take the stain; the chromosomes are found lying 

 in pairs often twisted around each other as before, as 

 seen in /. They pass in this condition on to the first 



