HETEROCHROMOSOMES IN MOSQUITOES. Ill 



In resting spermatogonia of Anopheles (Figs. 7 and 8) a con- 

 densed mass of chromatin varying in form is found associated 

 with a large plasmosome near the nuclear membrane. In Culex 

 there is nothing of the kind only a large central plasmosome 

 surrounded by an even spireme. In Anopheles there is a very 

 conspicuous contraction or synizesis stage (Fig. 9) in which the 



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_ ' *<""* f 



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8 



FIGS. 7 and 8. Anopheles punctipennis, resting spermatogonia. X =the hetero- 

 chromosome. 



FIG. 9. Synizesis stage. 

 FIGS. 10-12. Growth stages. 

 FIG. 13. Prophase. 



heterochromosome appears as a deeply staining mass of chromatin 

 resting against a ball of paler chromatin threads. The corre- 

 sponding stage in Culex ('10, Figs. 12 and 13) showed a ball of 

 chromatin thread wound about a plasmosome. In the later 

 growth stages of the spermatocytes of A nopheles, the heterochro- 

 mosome pair assumes a great diversity of forms. Occasionally, 

 especially in early stages, the unequal ends of the pair only are 

 fully condensed as shown in Fig. 10, which is a tangential section 

 of the nucleus. Fig. 1 1 shows a late spireme stage with hetero- 

 chromosome (x), plasmosome (p~) and parts of a pale spireme. 

 Fig. 12 is a late growth stage taken from a cyst where the cells 

 were mostly in metaphase of the first spermatocyte mitosis; 

 here the heterochromosome pair shows nothing of its composite 



