Pair of Heterochromosomes in Forficula 229 



during these stages. Sometimes it contains a vacuole as in Fig. 

 10, especially in late growth stages. In the preparations stained 

 with thionin the heterochromosomes can be distinguished from 

 the plasmosomes with comparative ease, on account of their dif- 

 ferent staining qualities. 



The spireme segments and splits longitudinally at about the 

 same time (Fig. 13). Sometimes the daughter segments spread 

 apart and twist as in Fig. 14, but they soon fuse again (Fig. 15) and 

 most of the segments assume the form of loops, U'sand twists (Figs. 

 15, 16, 17). Fig. 18 shows a variety of prophase forms. The 

 twists and figure 8's are formed from such loops as are seen in Fig. 

 15, and further condensation gives the U and ring forms. The U- 

 form is the most common (Fig 19), but rings and twists, and figure 

 8's with the ends twisted together are frequently seen. Figs. 20, 

 21, and 22 show transition stages from the rings and U's to the 

 dumb-bell form in which the chromosomes come into the spindle. 

 Occasionally one sees an incipient cross (Fig 21, a). Fig 22 shows 

 a variety of intermediate and transition stages. Fig 23 is a tan- 

 gential section of a nucleus in a late prophase, showing the hetero- 

 chromosome pair [x) and three ordinary bivalents. Figs. 24 and 

 25 also show late prophase stages. In Fig. 25 the tetrad charac- 

 ter of the bivalents is evident. In a spindle-prophase and meta- 

 phase, the tetrads are sometimes as clear as in Fig 26, both in thio- 

 nin preparations and also in preparations where the differentiation 

 of iron-haematoxvlin has been carried to just the right point. The 

 first spermatocyte metaphase usually looks like Fig. 27 from the 

 Eisenach material, or Fig. 28 from the Helgoland collection, the 

 heterochromosome pair being at one side of the plate and often 

 remaining out of the plate longer than the other pairs (Fig. 28). 

 Figs. 29 and 30 are earlier and later metaphase plates with the 

 heterochromosome ix) distinguishable at one side of each group. 

 In thionin preparations and in the paler iron-haematoxylin slides 

 one finds some spindles in which the tetrad nature of some of the 

 bivalents is shown both by longitudinal furrows and by the attach- 

 ment of the spindle fibers to the split ends of the dumb-bells (Fig. 

 31). A similar stage seen from the pole of the spindle is shown in 

 Fig. 32, some of the chromosomes showing the split. Fig. 33 gives 



